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>

plugin/hooks/scribe_prior_art.sh

@@ -111,10 +111,13 @@ if [ -n "$repo_root" ] && [ -n "$code" ]; then
         if (t != "") print "sym\t" t; next
       }
       # Keyword-announced definitions, functions and named types alike.
+      # Dunders are skipped: every class defines __init__, so "already defined
+      # in N other files" is guaranteed noise for them — and noise is what
+      # teaches sessions to skip the hint.
       if (match(line, /^(function|def|class|func|fun|fn|sub|struct|trait|interface|enum|object|protocol|type)[[:space:]]+[A-Za-z_$]/)) {
         t = line; sub(/^[a-z]+[[:space:]]+/, "", t)
         sub(/[^A-Za-z0-9_$].*$/, "", t)
-        if (t != "") print "sym\t" t; next
+        if (t != "" && t !~ /^__.*__$/) print "sym\t" t; next
       }
       # Arrow/expression assignment: const name = (…) / let name = async (
       if (match(line, /^(const|let)[[:space:]]+[A-Za-z_$][A-Za-z0-9_$]*[[:space:]]*=[[:space:]]*(async[[:space:]]*)?[(<]/)) {