feat(web): select a dashboard session from a #session=<id> link

A page that keeps one Codeman window open, such as a task board, could only
show a session by sending that window to /session/<id>, which loads the whole
app again for every click. The dashboard now reads a #session=<id> fragment
when it loads and on hashchange, selects that session, and removes the
fragment with history.replaceState so the next identical link is still a
change. Re-pointing a window that already shows the dashboard changes only the
fragment, so the page stays loaded and the switch is a tab change.

A link can name a session the dashboard does not list yet, because the page
that created it may link before session:created arrives. The id waits until
that event names it, and picking another tab yourself retires it.

Following a link is an app selection (`auto: true`). The page that set the
fragment may be a script, so it must not spend the session's idle alert.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/architecture-invariants.md

@@ -580,7 +580,7 @@ Either way the actual launch (`runCustomModelEntry`) routes through `run()` itse
 
 ⚠️ **Viewing a session ACKNOWLEDGES its idle item, it does not resolve it** (`POST /api/approvals/session/:sessionId/viewed` → `acknowledgedAt` → `approval:updated`): the item stays pending (still answerable, still Read My Mind context) and only stops arming the yellow tab alert. That flag is what makes the clear durable, since the view-clears-idle rule used to live in one browser's memory and `seedApprovals()` re-armed the alert on the next reload while other devices never heard about it at all; the local half is `markIdleAlertSeen()` (app.js), called from BOTH `selectSession` paths, including the already-active early return, where a click could otherwise never clear the alert.
 
-⚠️ **Only a HUMAN opening a session acknowledges**: `selectSession(id, { auto: true })` marks the three selections the APP makes (boot restore, a solo window opening its target, the fallback after the active session is closed) and skips the acknowledgement, so a page load cannot silently spend an alert the user never saw. The flag defaults to user-initiated, so an untagged call site fails toward acknowledging rather than toward an alert nothing can clear; `test/session-select-ack-gate.test.ts` pins both the gate and the tagged call sites. Idle-only by construction (`acknowledge()` defaults to `['idle']`): looking at a permission/question dialog does not answer it.
+⚠️ **Only a HUMAN opening a session acknowledges**: `selectSession(id, { auto: true })` marks the four selections the APP makes (boot restore, a solo window opening its target, a `#session=<id>` link from another page, the fallback after the active session is closed) and skips the acknowledgement, so a page load cannot silently spend an alert the user never saw. The flag defaults to user-initiated, so an untagged call site fails toward acknowledging rather than toward an alert nothing can clear; `test/session-select-ack-gate.test.ts` pins both the gate and the tagged call sites. Idle-only by construction (`acknowledge()` defaults to `['idle']`): looking at a permission/question dialog does not answer it.
 
 ⚠️ Same rule on the input path: `_ackDelivery` (app.js) spends the IDLE alert only, via that same `markIdleAlertSeen()`. It used to `clearPendingHooks(sessionId)` with no kind, so one keystroke wiped a RED alert on that device while the dialog was still up, the other devices stayed red, and a reload re-seeded it.