37: Register geo: protocol handler (manifest + optional runtime registration)

[Saber5656]

Derived from docs/issues/37-geo-protocol-handler.md — the canonical source of truth. Execution order & dependencies: docs/ISSUE_PLAN.md (PR #1). If this issue and the doc disagree, the doc wins.

Summary

Register chronomap as a geo: URI handler via manifest protocol_handlers (installed PWA) and an
opt-in registerProtocolHandler call (desktop browsers), both routing through /share.

Context

research/map-app-integration.md §1: geo is on the HTML safelist. This gives chronomap a
standards-based inbound path from any app emitting geo links (no share sheet needed).

Scope

• Manifest (30's config): protocol_handlers: [{ protocol: "geo", url: "share?text=%s" }]
  (base-relative; verify built form resolves to /chronomap/share?text=%s).
• Runtime (desktop): in AboutSheet (47) or MenuButton, an opt-in item i18n menu.registerGeo
  (geoリンクをこのアプリで開く) → navigator.registerProtocolHandler('geo', '{origin}{base}share?text=%s') guarded by feature detection + try/catch (some browsers
  restrict); success/failure toast. Shown only when the API exists.
• /share route (35) already handles text=geo:… — no new parsing.
• Document behavior matrix in docs/integrations/protocol-handler.md (10 lines: which
  browsers/OS honor manifest vs runtime registration, per research doc).

Detailed Requirements

1. Registration must never run automatically (user gesture + explicit menu action only).
2. The %s value arrives URL-encoded — confirm 35's route decodes exactly once (URLSearchParams
   does; add a regression test with double-encoded input expecting failure NOT double-decode).
3. No behavior change for browsers without support (item hidden).

Acceptance Criteria

• Built manifest contains the protocol_handlers entry with base-correct URL.
• e2e: simulate handler invocation by navigating /share?text=geo%3A35.68%2C139.76 → correct
  deep link (this also pins the single-decode contract).
• e2e: menu item hidden when API absent (override in test); visible + calls API when present
  (spy) with exact template string.
• Double-encoded regression test passes (goes to ImportSheet, not to wrong coords).

Validation

tests/e2e/protocol.spec.ts; manual desktop Chrome check recorded in PR (chrome://settings/handlers).

Dependencies

30 (manifest), 35 (route).

Non-goals

web+chronomap: custom scheme (unneeded), Android intent filters (n/a for PWA), auto-registration.

Design References

DESIGN §9.3; research/map-app-integration.md §1.