feat(app): SessionDetail polish + library-feed home

[graydawnc]

Why

Once the rest of the stack landed and the team started dogfooding, three pain points emerged together:

1. SessionDetail had no first-class actions. Resuming, copying the session ID, or copying the resume command all required leaving the page or hunting through context menus.
2. The library shell felt unfinished. The home feed (project-card grid from the search-migration PR), the section headers, the search results scope chip, alignment between sidebar wordmark and pane headers, and the Cmd+K overlay all needed a coordinated design pass.
3. in:project scope was a real bug. The chip was plumbed through the UI in the search-migration PR, but the IPC handler ignored the identityKey argument — search returned global results regardless of what the user picked.

Bundling them keeps each diff small while letting reviewers see the design pass as one cohesive change.

What this PR does

SessionDetail — header + actions

• Title row: back arrow + truncating title
• Meta line: path · N messages · time · ● source (source dot+label moved here from a separate chip; saves vertical space and groups all metadata)
• Actions row (right-aligned to meta, self-end): Pin · Resume in Terminal · ⋯
• Overflow menu (⋯): Copy session ID, Copy resume command (these are secondary actions — promoting them to the toolbar would crowd it without payoff)
• Back arrow aligned to the title's first line so it doesn't drift toward the meta row
• All MessageBubble rows pad to px-6 so message avatars line up with the back arrow

Library home — global feed

• Replaces the project-card grid with: Pinned segment (across all projects) → date-bucketed Recent (Today / Yesterday / Earlier This Week / Earlier)
• Hides empty (0-message) sessions because the watcher creates a session row when a CLI process starts, before any user input — those rows would otherwise pollute the feed
• Section headers are collapsible (chevron reveals on hover) — same component used in ProjectView

Sidebar shell

• Permanent search trigger (full-width pill) at the top
• PROJECTS list collapsible
• Settings gear pinned to bottom-right (icon-only, aligned with the project session-count column above)
• Sync status text reformatted to <count> sessions · <relative> (e.g. 420 sessions · 5m)
• Hides scrollbar (scrollbar-none) — Linear/Notion-style; kept overlay scroll behavior for trackpads
• New Settings → General section: Sidebar density toggles (Show source dots / Show session count) — for users who want a cleaner sidebar
• Refetches project_groups_v whenever sync phase changes, so newly-synced projects appear without a manual reload

Cmd+K overlay polish

• Recents in empty state: when query is empty, show recent sessions (scope-aware: scoped to the active project if in:project is selected) bucketed by date — Notion-style
• Stable height: min-h-[220px] max-h-[min(420px,55vh)] body so the overlay doesn't jitter when toggling Fast/Agent or scope, and doesn't get absurdly tall on small windows
• Mode-aware placeholder: "Search your sessions…" vs "Ask anything about your sessions…" so the user knows what the active mode does
• Refined SegmentedPill: drops the border/shadow look for an accent-tinted active state; adds role="tablist" + aria-selected
• Tab hint on scope: anchored to the scope chips so users discover the keyboard shortcut for in:project ↔ All toggle
• Agent selector (Agent mode only): rendered on the scope row, right-aligned with an "Asking:" label. Trigger uses mousedown.preventDefault so opening the menu doesn't steal focus from the input — Tab keyboard nav keeps working after closing the menu
• in:project IPC fix — the missing piece. searchFragments and the IPC handler now accept and apply the identityKey arg; doSearch passes it through when committing from the overlay; the results page header displays the active scope so the user can verify

Pin + ProjectView refinements

• PinButton redrawn (Tabler-style angled pushpin) with two sizes — md (16px in detail) and sm (11px in rows) so it doesn't out-weigh adjacent ⋯ menus
• ProjectView source filter: replaced separate pill row with inline opacity toggle on the meta source dots — clicking a source dims it (filters out); much less visual weight
• ProjectView sort uses the same Menu component as FragmentResults, for consistency

Alignment + small polish

• Unified pt-3 px-6 across panes so the sidebar wordmark, project header, library feed title, and session detail all start at the same vertical position
• ⋯ buttons everywhere use mousedown.preventDefault so a click doesn't keep focus and leave the action group stuck visible
• Folder icon prefix on each Sidebar project row; chevron reveals on hover
• New shared Menu component (reusable dropdown with click-outside + escape handling)

Test plan

• pnpm --filter @spool/app exec playwright test — all suites pass
• Manual: pin/unpin from session detail; copy resume command from menu; Cmd+K with project scope → "View all results" → verify scope label and results both reflect the project
• Manual: Cmd+K empty query → recents render (scope-aware); toggle Fast/Agent → no height jitter; open agent menu → Tab keyboard still works after closing
• Manual: Settings → General → toggle source dots / session count → sidebar updates immediately
• Manual: collapse/expand sidebar PROJECTS and home feed sections; verify alignment between sidebar wordmark, settings gear, and pane headers