feat(forge): adapter seam + Gitea implementation — optional read access to the operator's forge (#2689)

Step 4 of milestone 288 (decision #2686). services/forge.py defines the
contract steps 5-7 consume — read_file (content + last_commit_sha, the
provenance stamp), default_branch, resolve_repo, check — with GiteaForge
as the first implementation over the REST contents/repo/version/user
endpoints. Repo identity reuses normalize_repo_key: the host segment
selects whether this forge serves a recorded repo, the remainder is the
API path, so no new identity scheme exists. Read-only by construction;
errors never carry the token; first outbound-HTTP timeout convention
(5s total, no retries — the consumer's fallback is the retry policy).

OPTIONAL per instance (rule #115): get_forge() returns None when
unconfigured and every consumer treats None as today's behavior. Config
lives in admin settings (Settings → Config → Git Forge: kind/base
URL/token, save + test-connection probe reporting version + identity),
with FORGE_* env / Docker-secret fallbacks; DB wins so a UI edit can't
silently lose to an env var. Token treatment follows the smtp_password
convention (masked on read, mask-sentinel skipped on write, absent from
audit details) — and wiring it surfaced that the generic GET/PUT
/api/settings dump bypassed that masking for the owning admin's raw KV
rows, so secret keys are now masked there too (fixes the same exposure
for smtp_password).

Contract tests run against httpx.MockTransport as the fake forge — the
reference behaviors the GitHub adapter (step 8) must reproduce — plus
the off-by-default gate, partial-config-is-off, env-vs-DB precedence,
and route/mask structural checks. Also: the step-2 definition detector
learned to skip dunders after flagging __init__ as 'already defined in
4 files' on this step's own build — guaranteed noise for a hint that
must stay trustworthy.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/scribe/config.py

@@ -60,6 +60,15 @@ class Config:
     # the MCP layer doesn't proxy web search (Claude has its own).
     SEARXNG_URL: str = os.environ.get("SEARXNG_URL", "")
 
+    # Git forge integration (#2689) — optional read access to the operator's
+    # forge so snippet bodies can be fetched/verified server-side. Normally
+    # configured in Settings → Config (stored as admin settings); these env
+    # fallbacks exist so a deployment can keep the token in a Docker secret
+    # instead of the database. DB value wins when both are set.
+    FORGE_KIND: str = os.environ.get("FORGE_KIND", "")
+    FORGE_BASE_URL: str = os.environ.get("FORGE_BASE_URL", "").rstrip("/")
+    FORGE_TOKEN: str = _read_secret("FORGE_TOKEN", "FORGE_TOKEN_FILE", "")
+
     @classmethod
     def oidc_enabled(cls) -> bool:
         return bool(cls.OIDC_ISSUER and cls.OIDC_CLIENT_ID and cls.OIDC_CLIENT_SECRET)