feat: Presigned object URLs (s3 driver)

POST /buckets/:id/object-presigns mints SigV4 query-signed GET/PUT
URLs so clients move bytes directly against S3 — large transfers skip
the backend entirely.

- storage.Presigner optional interface; S3Store implements, local
  driver returns a clear error (no external surface to sign).
- TTL 60s–1h (default 15m); download requires read role + existing
  object row (no key probing); upload requires write role.
- S3_PUBLIC_ENDPOINT rewrites the client-facing host for internal
  S3_ENDPOINTs — signatures bind the host, URLs are valid only where
  minted.
- CLI: primora objects:presign <bucket> <key> [--upload] [--ttl].

Verified live against cloudserver: GET fetched the object with no
auth headers; PUT pushed 1 MB direct to S3; unsigned list → 403;
untracked-key download presign → 404.

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

CHANGELOG.md

@@ -25,6 +25,7 @@ All notable changes to Primora. Format follows [Keep a Changelog](https://keepac
 - **Email templates + send log** (`core.email_log`, migration 00014) — the mailer renders registered templates (currently `invitation`) and every send — successful or failed — is recorded with template, recipient, subject, status, and error text. `GET /projects/:id/emails` lists recent sends; the Members page shows an "Email log" card under pending invitations.
 - **S3-compatible object storage backend** — `BACKEND_STORAGE_DRIVER=s3` swaps the local disk store for any S3-compatible API (AWS, MinIO, Garage, R2) via a stdlib-only SigV4 implementation — no AWS SDK dependency. `S3_ENDPOINT`/`S3_REGION`/`S3_BUCKET`/credentials configure it; `S3_PATH_STYLE` (default on) covers MinIO/Garage, off for AWS virtual-hosted. The configured bucket is created on startup if missing; objects stream with computed SHA-256, `storage_path` records `s3://bucket/key`. Verified live end-to-end (bucket → put → get → copy → list → delete).
 - **Functions** (`core.functions` + `core.function_runs`, migration 00015) — project-scoped JS/TS executed by a runtime binary on the backend host (`bun` or `deno`, per function). The JSON payload arrives on stdin and as `PRIMORA_PAYLOAD`; stdout/stderr are captured per run (capped at 64 KiB) with status, exit code and duration — `FUNCTIONS_RUNTIME`/`FUNCTIONS_TIMEOUT_SECONDS`/`FUNCTIONS_MAX_OUTPUT_BYTES` configure the runner. API: CRUD under `/projects/:id/functions`, `POST …/invoke` (502 + recorded run on failure), `GET …/runs`. Dashboard gains a Functions page: code editor, JSON payload invoke, live result, run history. Code executes with backend privileges — the documented self-hosted trust model.
+- **Presigned object URLs** — `POST /buckets/:bucketID/object-presigns` mints SigV4 query-signed `GET`/`PUT` URLs (60 s–1 h TTL) so clients transfer large objects directly against S3 without proxying through the backend. Read role for downloads (object must exist — no key probing), write role for uploads. `S3_PUBLIC_ENDPOINT` rewrites the client-facing host for internal `S3_ENDPOINT`s; signatures bind the host so URLs are valid only where they were minted. The local driver returns a clear error — a presigned URL needs a real object API.
 - **Function triggers** (migration 00016) — three new ways to run a function, all through the same executor and run log. Scheduled jobs accept `function_id` instead of `url` (run status mirrors the exit code); inbound hooks gain `mode: "function"` — the received body becomes the function's stdin payload, acked immediately with the run recorded async; and `event_pattern` on a function (`document.*`, `*`, or an exact type) fires it detached whenever a matching domain event publishes — `{event, project_id, occurred_at, data}` as payload. Runs record trigger source: `manual`/`schedule`/`hook`/`event`. Dashboard: function event-trigger field, job target picker (URL or function), and inbound-hook function mode.
 
 ## [0.7.1] - 2026-09-23