test: cover features since 053a9c0d + repair test tooling

Add ~330 tests across server (Jest), client (Vitest), editor-ext (Vitest)
and packages/mcp (node:test) for the gitmost features added since
053a9c0d: AI chat, AI agent roles, public-share assistant, MCP per-user
auth, HTML embed, page templates/embed, realtime tree, tree
expand/collapse, and the AI-settings UI.

Test-tooling fixes (prerequisite, were silently hiding coverage):
- Repair 3 page-template specs broken by the 11-arg TransclusionService
  constructor; they never compiled, so template access-control / content
  -leak / unsync-strip coverage was fictitious.
- Build @docmost/editor-ext before server tests via a `pretest` hook;
  the stale dist omitted the new HtmlEmbed/PageEmbed exports (TS2305).
- Let jest resolve the .tsx email templates: add `tsx` to
  moduleFileExtensions and widen the ts-jest transform to (t|j)sx?.

Behaviour-preserving "extract pure core" refactors that the tests drive:
- server: resolveShareAssistantRequest + uiMessageTextLength
  (public-share controller), decideBasicGate + mapAuthResultToResponse
  (mcp), buildErrorAssistantRecord (ai-chat), jsonbObject export (roles).
- client: render-raw-html + shouldExecute/canEdit, decide-embed-state,
  page-embed picker utils, tree-socket reducers, open/close branch maps,
  isEndpointConfigured/resolveKeyField; buildTreeWithChildren now treats
  a permission-trimmed orphan as a root instead of crashing.

Deferred (need a test DB or HTTP harness, documented in the specs):
repo-level Postgres integration tests and the public-share XFF E2E.
Pre-existing DI/lib0-ESM suite failures are untouched and out of scope.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/integrations/ai/ai-error.util.spec.ts

@@ -58,4 +58,26 @@ describe('describeProviderError', () => {
     // 'e | response body: ' + 300 chars + '…'
     expect(out.length).toBeLessThan('e | response body: '.length + 305);
   });
+
+  it('uses the fallback for a numeric or boolean (non-object, non-string) error', () => {
+    // typeof number / boolean is neither 'object' nor a non-empty 'string', so
+    // the early branch returns the fallback verbatim.
+    expect(describeProviderError(500, 'AI stream error')).toBe('AI stream error');
+    expect(describeProviderError(0, 'AI stream error')).toBe('AI stream error');
+    expect(describeProviderError(true)).toBe('Unknown error');
+    expect(describeProviderError(false, 'fb')).toBe('fb');
+  });
+
+  it('statusCode present but message undefined => "<code>:" with no trailing space', () => {
+    // `${code}: ${undefined ?? ''}`.trim() collapses to just "<code>:".
+    expect(describeProviderError({ statusCode: 503 })).toBe('503:');
+    // The trailing space after the colon is trimmed away.
+    expect(describeProviderError({ statusCode: 503 }).endsWith(': ')).toBe(false);
+  });
+
+  it('object with neither message nor statusCode nor body => fallback', () => {
+    expect(describeProviderError({}, 'AI stream error')).toBe('AI stream error');
+    // An object carrying only unrelated keys is still treated as message-less.
+    expect(describeProviderError({ foo: 'bar' } as never)).toBe('Unknown error');
+  });
 });