Add native TetraID account menu

[tetranow]

What changed

• adds a failure-contained TetraID browser-chrome module
• repurposes the existing native account row instead of embedding web UI
• routes account activation to the TetraID auth endpoint rather than Firefox Accounts
• adds compact chevron styling and preserves an accessible state-specific label
• restores the reused row after Firefox Sync updates its hidden/class state

Why

AltZen needs a visible TetraID identity layer without replacing Firefox Sync internals or adding startup network work. The existing 1.0.31 runtime also contains stale CSS that does not include the chevron fix.

Impact

The app menu shows “Connect AltZen to your TetraID” with a compact chevron. Signed-in placeholder state uses the same compact action. Authentication remains proof-of-concept and account state is still pref-backed; real session/profile synchronization is intentionally outside this first scoped commit.

Validation

• node --check src/zen/common/modules/ZenTetraID.mjs
• git diff --check
• baseline launch of the local AltZen binary with a fresh profile

Build and updated runtime validation are still in progress.