fix(packets): Clear Filters must reset observer and type selection state

[dborup]

Problem

The Packets page keeps observer and packet-type selections in closure-owned selectedObservers and selectedTypes Sets. Clear Filters resets filters, local storage, and visible checkboxes, but does not clear those Sets and leaves the “All” entries visually unchecked.

The next observer/type click can therefore restore stale selections that appeared to have been removed.

Upstream reference: Kpa-clawbot/CoreScope#2015.

Acceptance criteria

• Clear both internal Sets and rebuild their menus from an empty state.
• “All Observers” and “All Types” are checked, with matching trigger labels/titles.
• URL, local storage, and filters retain no stale observer/type values.
• Existing hash, node, channel, language, time-window, region, and My Nodes filter behavior remains unchanged.
• Clear causes the appropriate packet reload/render exactly once.

Regression test

Select observer A and a type, clear, then select B/a different type and prove A/the old type does not return anywhere. Also cover repeated clears and SPA remounting.

Non-goals

No control redesign, API/database change, or deploy.

[dborup]

Draft PR #132 er klar til review.

• CI: grøn. Go Build & Test, Playwright E2E og Docker-build er success; Release, Staging og Badges er skipped.
• Rettelse: Clear tømmer nu selectedObservers/selectedTypes og genopbygger begge menuer, så "All" er afkrydset. Type-valg viser nu også Clear-knappen.
• Test: den nye test går fra 2/8 på master til 8/8, og test-clear-filters.js er nu registreret i CI.
• Browser: verificeret ved 1440 og 1024.

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Generated by Claude Code

[dborup]

Fixed by #132 (merged as 5f493f1d). The other filter handlers and the initial load still drop ?obs=/?viewPath= from detail URLs; that is tracked in #147.