Dismiss canvas when leaving a rail surface (CL-6819)

[TheGreatAxios]

Leaving Routines (or any other rail surface) via in-app nav now closes the canvas column. The create/edit routine sheet, profile card, and artifact pane all dismiss when the first path segment changes, so a compact layout that hid the column cannot resurrect it after returning to expanded.

Nested detail (/routines → /routines/:id) and query-only changes share a prefix and keep the pane.

Fixes CL-6819

[TheGreatAxios]

Self-review

Verdict: implementation is correct and well-tested — the route-prefix comparison correctly distinguishes a rail leave from nested detail/query-only changes, and the new suite covers all four canvas kinds plus the compact-layout resurrection case. No changes made.

• Route-prefix logic (inAppRoutePrefix, dismiss effect) — DISMISSED: verified against closeCanvasContent in packages/shell-layout/src/canvas-column-state.ts; correctly closes whichever of profile/artifact/routine is open and drops focus, without racing the tenant-switch effect.
• Test coverage — DISMISSED: all 6 new scenarios (rail leave for profile/artifact/routine, nested detail, query-only, compact layout) exercise real ShellChromeProvider state, not mocks.
• Pre-existing test close-canvas fired from a sibling of AppShell closes a canvas AppShell is showing — CONFIRMED-OPEN (not fixed): fails both in the full file and in isolation (bun test test/shell-chrome-wiring.test.tsx -t "close-canvas fired"), unmodified by this diff. Environmental/pre-existing, out of scope for this PR.

Targeted tests:

• bun test test/shell-chrome-wiring.test.tsx (run from apps/web) — 7 pass, 1 fail (pre-existing, unrelated to this diff)
• bun run typecheck — pass

[linear-code]

CL-6819