refactor(webui): remove standalone sessions page

[Open-Squilla]

Scope

Remove the standalone /sessions full-screen ledger now that session history and management live in the sidebar and chat.

Branch

Base branch: main

Issue

Linked issue: None

If None, reason: This is a UI consolidation change requested during review.

Release Note

Release note: NONE

Tests

Ruff: N/A

Pytest: N/A

Build: npm run typecheck

Regression tests: updated

Notes: npm run check:architecture and targeted router/overview unit tests pass. Full E2E was not run.

Maintainer Live Check

Maintainer live check: no

Surface: browser

Maintainer-only note: The legacy /sessions deep link redirects to /chat.

Safety

No secrets or private artifacts added.

Third-Party Origin

Third-party origin: none

Documentation Changes

• Links point to existing repository files or stable external pages.

[github-actions]

Merge queue CI: failure — run 34890704464, attempt 1.
Tested queue candidate: fc12922826ffa613f746a2261357056dfc4188da. This result belongs to that combined tree, not necessarily the PR's current head.

• Full offline tests (ubuntu-latest, desktop-installer-contracts): failure
• Windows high-risk (desktop-installer-contracts): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34892818773, attempt 1.
Tested queue candidate: 2776ced188248600998398ac0fc3e7aba8213e10. This result belongs to that combined tree, not necessarily the PR's current head.

• Windows high-risk (desktop-installer-contracts): failure
• Full offline tests (ubuntu-latest, desktop-installer-contracts): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34900499576, attempt 1.
Tested queue candidate: b3aee3995e0c3c7dacafa8e5b625d31b3ec5ab10. This result belongs to that combined tree, not necessarily the PR's current head.

• Full offline tests (ubuntu-latest, gateway-sqlite): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34945638360, attempt 1.
Tested queue candidate: 51b9fb80748c4879a82f760fa9332f48e9c65831. This result belongs to that combined tree, not necessarily the PR's current head.

• Windows high-risk (core): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34946043861, attempt 1.
Tested queue candidate: 26af5d02b1ed4417801646a020b6193e26766d36. This result belongs to that combined tree, not necessarily the PR's current head.

• Windows high-risk (core): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34955633362, attempt 1.
Tested queue candidate: 008397af4f58e6e50b8b8beea9f71c8f2da2adb1. This result belongs to that combined tree, not necessarily the PR's current head.

• Windows high-risk (desktop-installer-contracts): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: failure — run 34957842499, attempt 1.
Tested queue candidate: 295d6c5a7c20e3b5652dd55c7cfcf6867c403e56. This result belongs to that combined tree, not necessarily the PR's current head.

• Windows high-risk (recovery-migration): failure
• CI result: failure

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.

[github-actions]

Merge queue CI: success — run 35012114166, attempt 1.
Tested queue candidate: 3d7716f31ec241483309310bfc974d2ae710b72c. This result belongs to that combined tree, not necessarily the PR's current head.

The run summary lists reused suites and executed checks. A green PR check alone does not mean queue validation has passed.