feat(repos): git-fingerprint-based machine-independent repo identity

Add git_fingerprint (root commit SHA-1) to managed_repos as a stable,
machine-independent identifier — identical across every clone regardless
of checkout path, remote URL, or SSH alias.

- Migration n1i2j3k4l5m6: adds git_fingerprint column + non-unique index
  (non-unique to support repos that share ancestry via forks/splits)
- GET /repos/by-fingerprint?hash=<sha>[&remote_url=<url>]: lookup by
  fingerprint; optional remote_url disambiguates shared-ancestry repos
- GET /repos/by-remote?url=<url>: fallback lookup by remote URL
- consistency_check.py --here [PATH]: auto-detects repo slug from any
  local checkout via fingerprint (falls back to remote URL), then auto-
  registers host_paths[hostname] so subsequent runs need no override
- --all now includes repos with host_paths[current_hostname], not just
  those with local_path
- fix-consistency-here / check-consistency-here Makefile targets
- Fixed _api_get bug: httpx strips query strings when params={} is passed
- Backfilled fingerprints for 14 repos on this host

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/schemas/managed_repo.py

@@ -11,6 +11,7 @@ class RepoCreate(BaseModel):
     name: str
     local_path: str | None = None
     remote_url: str | None = None
+    git_fingerprint: str | None = None
     description: str | None = None
     topic_id: uuid.UUID | None = None
 
@@ -19,6 +20,7 @@ class RepoUpdate(BaseModel):
     name: str | None = None
     local_path: str | None = None
     remote_url: str | None = None
+    git_fingerprint: str | None = None
     description: str | None = None
     topic_id: uuid.UUID | None = None
     last_state_synced_at: datetime | None = None
@@ -40,6 +42,7 @@ class RepoRead(BaseModel):
     local_path: str | None = None
     host_paths: dict = {}
     remote_url: str | None = None
+    git_fingerprint: str | None = None
     description: str | None = None
     status: str
     topic_id: uuid.UUID | None = None