fix(packets): preserve observation selection in detail URLs

[n30nex]

Red commit: c165087 (CI assertion failure).

Fixes #2091.

Packet detail links now retain the selected observation when page initialization or filter changes rebuild the URL. Initialization also restores obs from the complete hash after the router strips its query. Explicit ID links render the requested observation and retain it in Copy Link state.

The shared updater reads selection from the current route, so returning to the list or selecting another packet cannot resurrect an old observation. Existing filter serialization and Clear Filters behavior remain intact. No new requests, configuration, dependencies or layout changes.

Validation

• Real fixture browser checks use nondefault observation 502: hash/ID load, type/observer/time-window changes, refresh, Clear, and another refresh. Both URL and selected row are asserted.
• All 183 standalone frontend suites passed; focused filter browser suite 11/11.
• Broader local core run reached the unrelated Live input readiness bug bug(live): node filter accepts input before its handler is ready #2094, reproduced on unchanged master. The complete CI browser suite passed.
• ESLint 8: zero errors; 91 existing warnings. XSS diff, syntax and whitespace checks passed.
• Three independent reviews found no production defects; assertions additionally prove filter controls changed before checking selection.

E2E assertion added: tests/e2e/test-filter-ux-e2e.js:179.

OpenClaw profile/external preflight were unavailable; Chromium and repository checks ran directly. Local navigation used a 60-second budget. Final CI passed at 280ced5, including Go, browsers, coverage and both container architectures (run).

[n30nex]

Review feedback addressed (commit 280ced5):

1. Browser tests now prove type, observer and time-window controls changed before checking that the selected observation survives.
2. Both hash and explicit-ID routes are checked through load, filters, Clear and refresh using the real fixture's nondefault observation.

The implementation is a671a59; all 183 standalone suites and 11 focused browser checks passed. The broader local run exposed unrelated baseline bug #2094. This remains a draft pending final CI; the test-only commit's expected six assertion failures are recorded in run 36644030012.