Seed-packet capture: vision model, extraction, catalog match, create (backend) (#81)

Photograph a seed packet → it fills in the plant and the purchase. This is the
backend; the scan UI is a follow-up PR.

Vision model config (mirrors the agent model from #79):
- Migration 0011 adds instance_settings.vision_model; PANSY_VISION_MODEL is the
  env default. Precedence Settings → env → empty; the KEY stays in the env.
- EffectiveVision resolves it; /capabilities advertises "vision" only when a
  model + key are configured, so the UI offers the scan button only when it works.

Extraction is one-shot, NOT an agent loop (internal/vision):
- majordomo.Generate[SeedPacket] derives a JSON schema from the struct tags and
  hands the image to the vision model; it can't call a tool, so it can't touch
  the garden — it only reads a picture and returns data. Numeric fields are
  pointers, so a field the packet doesn't print comes back nil, not a made-up 0.
- Hermetic test: majordomo's fake provider returns canned packet JSON and
  Generate unmarshals it, image + derived schema included. No live model.

The image is normalized to JPEG at the upload boundary (imagenorm from #80),
which is where an iPhone HEIC becomes readable — majordomo's media path can't
decode HEIC. imagenorm now links into the binary (~7 MB, the cost #80 deferred).

The hard part is catalog matching, not OCR (internal/service/seed_packet.go):
- A wrong auto-match splits a variety's seed-lot history across duplicate rows,
  so the service NEVER auto-creates. matchPlants surfaces RANKED candidates
  (exact name → variety-in-name → same species, conservative and name-based),
  the user confirms, and CreateFromPacket makes the plant (new or existing) + the
  lot. Exactly one of plantId/newPlant, refused otherwise.
- Plants/lots aren't in the undo history (catalog/inventory), so no change set.
- The extractor is injectable (service.WithPacketExtractor) so ExtractSeedPacket
  and the /scan endpoint test end to end against a fake, no live model.

Endpoints: POST /seed-lots/scan (multipart image → proposal, reads only; extends
the read deadline for a slow phone upload, caps the body, maps too-large/unreadable
to clear statuses) and POST /seed-lots/from-packet (confirmed proposal → 201).

Docs: README (PANSY_VISION_MODEL), DESIGN (routes + the decision and why the
model can't touch the garden).

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01H3zbym8Doka2d7D48maSgZ

DESIGN.md

@@ -12,6 +12,7 @@ Work is tracked in Gitea issues; the tracking epic links every piece in dependen
 - **Users:** multi-user with ownership. Users own gardens; a garden can be shared with other users as viewer (read) or editor (edit content). Owner additionally shares/deletes. The first registered user is `is_admin` (set race-free inside the INSERT); admin gates instance-wide Settings (`requireAdmin`), the only thing that reads that flag.
 - **Auth:** OIDC-first (Authentik is the primary IdP), local argon2id passwords as an optional fallback.
 - **Instance settings (#79):** admin-editable, instance-wide config in a single-row `instance_settings` table — pansy's first DB-stored *instance* state (everything else hangs off a garden/object). Today it holds the agent model + on/off; **secrets never move here** — `OLLAMA_CLOUD_API_KEY` stays in the env so it doesn't land in backups or the undo history. Precedence: Settings value → env → default. The live agent Runner sits behind an `atomic.Pointer` in the API layer (`agentHolder`) with its routes always registered, so a settings change swaps it with no restart and no race against in-flight requests; `/capabilities` reads that pointer, so it reports what's live rather than what was configured at boot. The model/registry knowledge lives in one leaf package (`internal/agentmodel`) that both the runner and the settings validator import — agent imports service, so it can live in neither.
+- **Seed-packet capture (#81):** photograph a packet → a *vision* model (separate `vision_model` setting) reads it into structured fields via one-shot `majordomo.Generate[SeedPacket]` — NOT an agent loop, so the extraction can't touch the garden; it only reads a picture and returns data. The image is normalized to JPEG at the upload boundary (`internal/imagenorm`: decodes HEIC/webp/png/jpeg, since majordomo's stdlib media path can't do HEIC — the iPhone default). The hard part is **catalog matching, not OCR**: a wrong auto-match splits a variety's seed-lot history across duplicate rows, so the service NEVER auto-creates — it surfaces ranked candidates (`matchPlants`) and the user confirms, then `CreateFromPacket` makes the plant (new or existing) + the lot. Plants/lots aren't in the undo history (they're catalog/inventory), so there's no change set to wrap. The extractor is injectable on the service (`WithPacketExtractor`) so the whole path tests hermetically against majordomo's `fake` provider.
 - **Agentic future:** integration with majordomo/executus via typed Go tools (`llm.DefineTool[Args]`) wrapping the same service layer the REST API uses — not MCP/OpenAPI.
 
 ## Domain model
@@ -69,12 +70,14 @@ POST /objects/:id/fill        ← hex-pack a region with one plant; region by co
 POST /objects/:id/clear       ← soft-remove every active plop, as ONE change set
 GET,POST /plants              PATCH,DELETE /plants/:id            (own plants only)
 GET,POST /seed-lots           GET,PATCH,DELETE /seed-lots/:id     (own lots only; private)
+POST /seed-lots/scan          ← multipart image → a seed-packet proposal (reads only, no writes)
+POST /seed-lots/from-packet   ← confirmed proposal → a plant (new or existing) + a lot
 GET,POST /gardens/:id/journal PATCH,DELETE /journal/:id           (editor writes; author edits own)
 GET  /gardens/:id/journal/counts  ← entries per object, for the "has notes" indicator
 POST /agent/chat              ← SSE: step events, then the finished turn (editor only)
 GET,DELETE /gardens/:id/agent/history                             (the actor's own thread)
 GET  /capabilities            ← what this instance can do RIGHT NOW (tracks the live agent, not just config)
-GET,PATCH /settings           ← instance-wide config (admin only): agent model + on/off
+GET,PATCH /settings           ← instance-wide config (admin only): agent model + on/off, vision model
 GET,POST /gardens/:id/shares  PATCH,DELETE /gardens/:id/shares/:userId    (invite by email)
 GET,POST,DELETE /gardens/:id/share-link   ← the public read-only token for this garden
 GET  /public/gardens/:token   ← UNAUTHENTICATED read-only /full; the token is the capability