feat(dash): chat moves to /chat, /dashboard becomes system overview

[thinmintdev]

Summary

Overhauls the chat surface UX + restructures the main dashboard.

• Chat moves to its own #chat route (sidebar entry added). The ChatActive + ChatEmpty split collapses into a single ChatPanel + page-level ChatView; the legacy names stay as thin wrappers for the Tweaks-panel composer-state preview / screenshot harness.
• #hardware route is retired; its HardwareSection now lives on /dashboard alongside SnapshotStrip, MemoryMap, ThroughputCard, HealthCard. Sidebar + BottomTabs + TopBar labels updated to match.
• Composer boundary fix: typing surface wrapped in a .composer-input-card with var(--line) border + var(--accent-line) focus-within ring (the prior borderless textarea read as page background).
• Reasoning toggle in the chat header — pill control, OFF by default, persisted to localStorage["hal0.chat.showReasoning"]. Streaming continues to populate m.reasoning regardless, so flipping on mid-conversation retroactively reveals prior thinking. Gates ReasoningBlock render only.
• New-chat button now calls useChat.clear() (aborts in-flight + clears messages) instead of window.location.reload().
• Popout button opens #chat?popout=1 in a 480x760 popup window. parseRoute parses the hash query string; App short-circuits all chrome (TopBar, Sidebar, Footer, BottomTabs, Banners, Tweaks, modals) when popout=1.

Files

ui/src/dash/chat.jsx      | 442 +++++++++++++++++++++++++---------------------
ui/src/dash/chrome.jsx    |   7 +-
ui/src/dash/dashboard.jsx | 172 ++++++++++++++-----
ui/src/dash/extras.jsx    | 111 +--------------
ui/src/dash/main.jsx      |  50 +++++-
ui/src/dashboard.css      | 103 +++++++++-
6 files changed, 509 insertions(+), 376 deletions(-)

Test plan

• npm run build clean (verified locally: 119 modules, 538 kB JS, 86 kB CSS)
• ruff check src tests + ruff format --check src tests clean (Python untouched)
• /#dashboard renders the full hardware spread on the left + SnapshotStrip/MemoryMap/Throughput/Health on the right
• /#chat renders the chat surface; sidebar Chat entry is active
• /#hardware falls back to dashboard (route table no longer accepts it)
• Composer input has a visible border; focus draws an accent ring
• Reasoning toggle defaults OFF; reload keeps the preference; flipping on after streaming reveals prior reasoning
• New-chat button clears messages without reloading
• Popout button opens a small window at #chat?popout=1 with no sidebar/topbar/footer

Known follow-ups (not blocking)

• MessageList reasoning-only fallback ("see thinking above") is misleading when the toggle is OFF — minor copy fix.
• composerState Tweaks-panel selector + chatState="active"|"empty" props on DashboardView are dead after this change (only "skip" still routes). Cleanup pass worthwhile.
• New Storage HwCard in HardwareSection uses placeholder mock copy — not yet wired to /api/hardware.

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