feat(ui): consolidate the desktop design system

[kitlangton]

Why

The GPUI app had grown four visual dialects. Text came in 11 explicit sizes plus GPUI's inherited 16 px, so inputs and transcript bubbles looked like a different app. There were 7 button looks and 35 raw colour literals sitting beside 18 tokens. Section labels were in all caps, the product was called "HEX", and list cards overhung the header rule by 12 px. A .truncate() row could clip mid-glyph or collapse to "…". Every new pane added another helper because nothing said which one to use.

What Changes

• Tokens: src/design_tokens.rs is now the only place a raw colour, type size, line height, radius, or control height is written. The V2 surface colours are unchanged. The old FAINT (#6e6e6e) text was below 4.5:1 on cards, so it merges into TEXT_TERTIARY (#969696) and survives only as TEXT_DISABLED.

• Type scale: five steps, applied with .text_caption() … .text_title(). Each step sets its own line height, and the window frame sets BODY, so unsized text and inputs are 13 px.

  Step	Size / line	Use
  Caption	11 / 14	metadata, tags, section labels
  Footnote	12 / 16	descriptions, control labels
  Body	13 / 18	window default, values, inputs, row titles
  Headline	15 / 20 semibold	card, detail, and dialog titles
  Title	20 / 26 semibold	pane titles

• Components: src/desktop_ui.rs now has one button system: button / small_button / icon_button × Primary, Secondary, Ghost, Danger. Primary is the single accent fill, used for at most one action per screen, so the white meeting buttons are gone. There is also one non-interactive tag, plus menu / menu_item, pane_list / pane_detail, error_panel, empty_state, and truncated_line. Every superseded helper is deleted: header_button, canvas_button, compact_*, meeting_action_button, pane_list_card, and others.

• Geometry: one PANE_GUTTER is shared by the header and the body, so cards line up with the header rule. Controls are 30 px (24 px small).

• Truncation: truncated_line shapes its text at paint time against its final width, so lines end in "…" instead of clipping or keeping a provisional width.

• Copy: sentence case everywhere ("Stop & transcribe", "Permissions needed", "Open settings"). The product is "Hex" in window titles, menus, and copy. Duplicate state words beside toggles are gone. Native macOS menus keep title case.

• Icons: one Icon set of line-weight SF Symbols at medium weight. No .fill navigation symbols, no "×" or "+" text glyphs, and a globe instead of letter monograms for web pages.

• Meeting capsules: they use the shared tokens and buttons. The 2 px countdown bar and the "· 600s" suffix are removed. The 20 s timeout is unchanged.

• Docs: docs/design-system.md documents the tokens, which component does which job, the copy and icon rules, verification, and the full before → after audit. In AGENTS.md, the two desktop-UI invariants are replaced by a short mandatory pointer to it. design_tokens::tests::desktop_sources_use_tokens_instead_of_raw_styles fails on raw colours, sizes, line heights, radii, or .truncate() in desktop sources.

Behaviour, entry points, and debug selectors are unchanged. The dictation HUD is untouched.

Meetings actions and accent colour

• Overflow menu: the Meetings detail shows Copy transcript and Rename, plus a … button. Its menu holds Copy summary, Reveal Markdown/files, and Summarize/Regenerate summary ("Summarizing…" is shown disabled while it runs), then Delete… in red after a separator. It's built from new shared pieces: dropdown_menu, danger_menu_item, disabled_menu_item, menu_separator, and Icon::Ellipsis. Delete… keeps its two-step confirmation: the Trash button and Cancel replace the action row until you pick one. Copy summary keeps the menu open so "Copied" stays visible. Visibility and refusal rules haven't changed: nothing is offered while a meeting is recording or transcribing, and Delete is hidden while notes are being written. New preview flag: --open-meeting-actions.
• Accent: "Stop & transcribe" is now a Secondary button with a red dot and the elapsed time, matching the Recording tag. The sidebar "Update" is Secondary with an accent dot. Primary blue is left on one action per screen at most: Start recording, Choose model, or a dialog's confirm. Capsules count as their own screen. The rule is written down in docs/design-system.md (Rules 6–7, Colour) and in the AGENTS.md pointer.

Polish pass

• Shared detail header: Meetings, History, and Commands details all use one detail_header(detail_title, meta, actions) over a detail_body. Each has the same insets and an edge-to-edge rule under the actions. History used an inset rule before, and Commands had none.
• Section labels: they now line up with the text inside their cards (px_4) in Settings, Voice Action, the setup sheet, and Modes. Before, they sat 4 px in from the card edge, which matched nothing.
• Baselines: the new baseline_offset(LARGER, SMALLER) token puts the History timestamps on the title baseline (they sat about 3 px high) and detail_row labels on the value baseline.
• List group labels: a single list_section_label is shared by Meetings and Commands. The first group in Commands used to start 8 px lower than the first group in Meetings.
• Empty states: pane_list centres its empty message vertically, like the detail placeholder beside it.
• Commands: the "Current context" footer under the list is now a detail row. The list and detail cards now end at the same bottom edge.
• Transcript speaker labels: they line up with the text inside the bubble, not 4 px in from its rounded edge.
• Left / Either / Right: the segments are wider (40/50/40), and the control's width is calculated from them. Before, the selected pill ran into "Right".
• Menus: there's one MENU_WIDTH and one MENU_OFFSET for the history retention, microphone, mode context, and meeting menus. Before they used 148, 160, or 220 px with a literal 4 px offset.
• Icon optical size: Ellipsis is drawn one size up so its dots look as heavy as the other glyphs.
• Copy: "..." becomes "…" in placeholders and empty states. One-phrase row descriptions no longer end with a period; two-sentence descriptions keep theirs.

Demo

Release-build previews (voice-control preview …) on a MacBook Pro. Before is main 1c3dacf. After is the head of this branch. The full contact sheet is at ~/Library/Caches/hex-design/index.html.

Verification

cargo fmt --check
git diff --check
cargo clippy -j 2 --all-targets --all-features -- -D warnings
cargo test -j 2 --bin voice-control -- design_tokens desktop_ui app_window meeting_watcher
cargo build --release --bin voice-control -j 2   # MacBook Pro, then 19 preview captures

• macOS fmt, clippy, and git diff --check pass, and 59 targeted tests pass. New tests: meeting_overflow_menu_opens_beside_the_visible_actions, history_detail_rows_keep_their_values_on_one_line, detail_rows_fill_a_detail_body, and baseline_offset_lowers_smaller_text_onto_the_larger_baseline. The existing tests still cover contrast, the raw-style guard, and truncation layout.
• I compiled only for macOS, not linux_app.rs locally. Linux CI covers it.
• Captures caught a regression in the History detail rows on the real text system that the test platform's metrics didn't show: values first collapsed, then overflowed. The fix keeps detail_body a block. It's verified by a fresh capture.