feat(console): add go usage endpoint - #16513

The local-DB probe only sees this machine's messages and guesses at the
server's cost accounting, so its numbers diverged from the opencode.ai
dashboard. opencode now exposes GET /zen/go/v1/usage (anomalyco/opencode#16513),
which returns the same rolling/weekly/monthly percentages and reset times
the dashboard shows.

- Add OpenCodeCredentialLoader: reads OPENCODE_API_KEY or the
  `opencode-go` / `opencode` entry from $XDG_DATA_HOME/opencode/auth.json
- Add OpenCodeAPIUsageProbe: calls the endpoint with a bearer key, maps
  used% -> remaining%, 401 -> sessionExpired, 403 -> subscriptionRequired
- Keep OpenCodeUsageProbe (local DB) as a fallback when no key is present

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01CdVhUZgY4SKaYkuxdqR3AY

Upstream v1.18.16 (a3647eb) -> v1.18.17 (02546df), 32 commits.

Functional changes:
- fix(compaction): clearer instructions for smaller models like dsv4 flash (anomalyco#42045)
- fix(provider): add Merge Gateway reasoning variants (anomalyco#41867)
- fix(opencode): cap session retries with jitter (anomalyco#41939) - retry policy
  gains RETRY_MAX_RETRIES=5 global cap and 25% jitter
- fix(opencode): detect Copilot PDF input support (anomalyco#41522)
- fix(provider): scope DeepSeek V4 Flash sampling defaults (anomalyco#41620)
- fix(session): route all Muse family models to the Meta system prompt (anomalyco#41581)
- fix(app): use current default model (anomalyco#38603)
- feat(console): add go usage endpoint (anomalyco#16513) and r2 data catalog stats
- fix(ui): correct OC-2 weak icon color (anomalyco#41504)
- fix(i18n): use widely recognized developer terminology (anomalyco#41532)

Conflicts resolved: 30 package.json version bumps (rebranded 1.18.17-sscity),
bun.lock (took upstream, rebranded workspace entries via bun install), and
session/retry.ts (kept fork per-reason maxAttempts cap alongside upstream
RETRY_MAX_RETRIES global cap and jitter).

Co-authored-by: vimtor <[email protected]>

Co-authored-by: vimtor <[email protected]>

Co-authored-by: vimtor <[email protected]>

Co-authored-by: vimtor <[email protected]>

Co-authored-by: vimtor <[email protected]>

GET /zen/go/v1/usage merged in anomalyco/opencode#16513 and now answers
in production, so the parser no longer has to guess. The route returns
`{ usage: { rolling, weekly, monthly } }`, each window holding a status,
a floored percent and an ISO reset, and nothing else; the aliases and
dollar fallbacks written against the proposal are gone. A window marked
`rate-limited` reads as spent, since its floored percent can say 99.

A valid key on a workspace without Go answers 403 with an
EntitlementError, which now reads as no subscription instead of a
rejected key, and a 404 is drift rather than an outage. The cookie
still ranks above the key because only the console publishes dollars.

Co-authored-by: vimtor <[email protected]>