feat: session sharing frontend (#76)

* feat: add session sharing types, API client, and utilities

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add SessionTimeline and ActionMenu reusable components

SessionTimeline extracts timeline/checklist rendering from SessionDetailPage
into a reusable component for both authenticated and public session views.
ActionMenu provides a dropdown action menu with keyboard/click-outside dismiss.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add ShareSessionModal and integrate into SessionDetailPage

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add Share Progress popover to TreeNavigationPage

Replace the single "Copy for Ticket" button with a "Share Progress"
popover that offers three actions: Copy Progress Summary (existing PSA
export flow), Copy Share Link (auto-creates account-only share if
needed), and Manage Share Links (opens ShareSessionModal).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add public SharedSessionPage with tree preview

Add the public-facing shared session page at /share/:shareToken that
renders shared sessions without authentication. Includes error handling
for 401 (redirect to login), 403 (access denied), 404 (not found),
and 410 (expired). The page features a minimal header, session metadata,
SessionTimeline component, and a new SharedSessionTreePreview component
that renders the decision tree structure with the path taken highlighted.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: add My Shares management page with nav link

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: address code review issues in session sharing

- Add useCallback for loadShares in ShareSessionModal (React hook deps)
- Use TreeStructure type instead of Record<string, unknown> for type safety
- Fix login redirect format to match LoginPage's expected state shape

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* test: add focused tests for session sharing utilities and API

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: resolve tree_structure type compatibility for shared session views

- Use TreeStructure & Record<string, unknown> intersection for JSONB flexibility
- Add explicit cast in SharedSessionTreePreview for recursive node rendering

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* docs: add session sharing learnings to CLAUDE.md

Add gotchas #12 (TreeStructure vs Tree types) and #13 (login redirect
state format), note about npm run build strictness, and public route
pattern to Common Tasks.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat: procedural editor UX improvements

Add URL intake field type, fix variable name editing collapsing fields
(index-based keys/updates), auto-generate variable names by field type,
add section header as first-class step type, and simplify step editor
with "More Options" collapsible for advanced fields.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: allow section_header step type in validation, improve tag input

- Add 'section_header' to VALID_STEP_TYPES in backend validation so
  procedural flows with section headers can be published
- Replace procedural editor's inline tag input with TagInput component
  (supports autocomplete, Tab, comma, semicolon, and paste splitting)
- Add semicolon delimiter support to TagInput component

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: add type-aware routing for procedural flows

Centralizes tree navigation routing via getTreeNavigatePath helper.
Fixes all pages to route procedural sessions to /flows/:id/navigate
instead of /trees/:id/navigate. Adds safety redirect in troubleshooting
navigator and resume support in procedural navigator.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix: remove unused index prop from IntakeFieldEditor

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/pages/TreeLibraryPage.tsx

@@ -15,6 +15,7 @@ import { TreeTableView } from '@/components/library/TreeTableView'
 import { ViewToggle } from '@/components/library/ViewToggle'
 import { SortDropdown } from '@/components/library/SortDropdown'
 import { cn, safeGetItem } from '@/lib/utils'
+import { getTreeNavigatePath } from '@/lib/routing'
 import { usePermissions } from '@/hooks/usePermissions'
 import { useUserPreferencesStore } from '@/store/userPreferencesStore'
 import { toast } from '@/lib/toast'
@@ -450,7 +451,7 @@ export function TreeLibraryPage() {
                   </div>
                   <div className="flex items-center gap-2">
                     <button
-                      onClick={() => navigate(`/trees/${s.tree_id}/navigate`, { state: { sessionId: s.id } })}
+                      onClick={() => navigate(getTreeNavigatePath(s.tree_id, s.tree_snapshot?.tree_type), { state: { sessionId: s.id } })}
                       className="flex items-center gap-1.5 rounded-md bg-white px-3 py-1.5 text-sm font-medium text-black hover:bg-white/90"
                     >
                       <Play className="h-3.5 w-3.5" />