Replace the runtime "which sidebar" switch with Next.js's native
nested-route-group layouts. Eliminates the P1 unmount/remount
jitter: moving between /chat and any other workspace route no
longer destroys and rebuilds the sidebar subtree, because the two
sidebars now live under sibling route segments whose layouts mount
once each.

Structure:
  (workspace)/
    layout.tsx              — UnifiedChatProvider + flex container
    (nav)/                  — routes that share WorkspaceSidebar
      layout.tsx            — WorkspaceSidebar + <main>
      page.tsx              — homepage (moved)
      agents/, book/,
      co-writer/, playground/
    chat/
      layout.tsx            — OutlineSidebar (mock) + <main>
      [[...sessionId]]/

Changes:
- (workspace)/layout.tsx: sheds both the sidebar and the old client-
  side pathname-sniffing wrapper. Now trivially a server component.
- (workspace)/(nav)/layout.tsx: new; renders the main nav sidebar.
- (workspace)/chat/layout.tsx: new; renders the outline sidebar
  with a MOCK_OUTLINE placeholder (TODO marker for phase 5 swap).
  The mock outline is shorter now that we only spell the fields
  that differ per-row; shared defaults are filled via a .map().
- components/sidebar/ContextualSidebar.tsx: deleted. The client
  pathname switch it implemented is made redundant by Next.js's
  segment-level layouts.

This also dissolves P1 HKUDS#2 (startsWith-too-greedy) by construction —
there is no longer any pathname comparison to get wrong.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

…ss /space

Phase 0.5 audit follow-up HKUDS#2. SpaceSectionHeader carried `text-[19px]`
which is off the canonical typography scale (24/20/18/16/14/12 px).
NotebooksSection also had two `text-[13.5px]` h2s. Both flagged in the
audit as 4× leakage (one helper consumed by 4 sub-routes).

Changes:

  components/space/SpaceSectionHeader.tsx (deleted)
    - Removed entirely; functionality fully covered by PageHeader.

  components/space/{Notebooks,QuestionBank,Skills,Memory}Section.tsx
    - Replace <SpaceSectionHeader> with <PageHeader> from
      @/components/layout. h1 now text-2xl font-semibold per the
      canonical scale.
    - SkillsSection + MemorySection rename `action={...}` → `actions={...}`
      to match PageHeader's API.
    - Drop the `import SpaceSectionHeader` line from each.

  components/dev/showcases.tsx
    - Replace SpaceSectionHeaderPreview with PageHeaderPreview (same
      shape, canonical sizes). Registry entry id renamed
      "space-section-header" → "ui-page-header" under category
      "UI 原语" / categoryCode "layout/" — PageHeader is a layout
      primitive, not space-specific.

  components/dev/DevDashboard.tsx
    - Update the structural tree dump: drop SpaceSectionHeader.tsx
      line + decrement space/ count 6 → 5.

Visual baselines updated:
  - /space/notebooks darwin × light/dark — h1 19→24px, icon chrome
    muted-bg, no border-b. (Linux baseline shows loading spinner;
    docker container can't reach BE proxy through host.docker.internal,
    so the post-load state never renders. Same documented limitation
    as previous /space commits.)
  - /dev?view=showcase darwin/linux × light/dark — registry entry
    swap.
  - /dev?view=gallery|tree linux — sub-tolerance pixel drift from
    --update-snapshots=all.

Verification: 123 checks green (0 lint errors / 0 typecheck /
83 node / 18 component / 5 desktop smoke / 5 mobile smoke /
12 visual). Phase 0.5 carry-over status:
  ✅ /chat visual baseline (commit 6e24e0a)
  ✅ SpaceSectionHeader → PageHeader (this commit)
  ⏳ InspectorPanel decision
  ⏳ PageHeader applicability docs

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Issue HKUDS#2: Add knowledgePointsLabel locale key for standalone label usage
instead of reusing number-suffix key ('个知识点' → '知识点').

Issue HKUDS#3: Delete 9 empty auto-generated test modules cluttering /learning
page (retain 'default' with 3 modules and 'init3').

Issue HKUDS#4: Default manual book ID to empty string instead of 'manual'
to avoid leaking implementation detail to users.

…etection

avoid false 'Virtual env not detected' warning under conda

Issue HKUDS#2: Add knowledgePointsLabel locale key for standalone label usage
instead of reusing number-suffix key ('个知识点' → '知识点').

Issue HKUDS#3: Delete 9 empty auto-generated test modules cluttering /learning
page (retain 'default' with 3 modules and 'init3').

Issue HKUDS#4: Default manual book ID to empty string instead of 'manual'
to avoid leaking implementation detail to users.