feat(deployments): field-capture endpoint for pending deployments (commit 1)

Field-install workflow needs to be fast: arrive on site, snap a photo
of the seismograph in place, leave.  Project / location classification
happens later at a desk.  This adds the data model + capture endpoint
for that workflow.

Data model
- New PendingDeployment table.  Lifecycle: awaiting → assigned (when
  promoted to a real UnitAssignment) or → cancelled (operator's
  mistake).  Photos are filesystem files under data/photos/{unit_id}/
  with the filename stored on the row.
- Migration: backend/migrate_add_pending_deployments.py (idempotent).

Endpoints
- POST /api/deployments/capture  — multipart upload (unit_id, photo,
  optional note).  Refuses non-seismographs.  Extracts EXIF GPS
  (cribbing extract_exif_data from routers/photos.py) and stores
  the captured "lat,lon" on the row.  Saves the photo under
  data/photos/{unit_id}/install_YYYYMMDD_HHMMSS_<uuid8>.<ext>.
  Returns the new pending_deployment_id + extracted coords + photo
  URL for the client to render confirmation.
- GET  /api/deployments/pending           — list by status (default awaiting)
- GET  /api/deployments/pending/{id}      — single row detail
- POST /api/deployments/pending/{id}/promote — classify → create
  UnitAssignment.  Body accepts two shapes: assign-to-existing-location
  OR create-new-location (with new-or-existing project).  Sets
  status=assigned, resulting_assignment_id, promoted_at.
- POST /api/deployments/pending/{id}/cancel  — abandon with optional reason.

All four routes write UnitHistory audit rows
(pending_deployment_captured / _promoted / _cancelled).

Events from a unit with an unclassified pending deployment land in the
unit's "Unattributed" events bucket as usual.  Once promoted, the new
UnitAssignment's window retroactively attributes them — same mechanism
the metadata-backfill tool uses.

Seismograph-only for v1.  SLM deployments don't follow this pattern
and are tracked elsewhere.  Capture refuses non-seismograph unit_ids
with HTTP 400.

UI (commits 2 + 3) lands next.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

backend/migrate_add_pending_deployments.py

@@ -0,0 +1,75 @@
+"""
+Migration: add `pending_deployments` table.
+
+Stores "I just installed this seismograph" captures from the field.
+A pending deployment is the prospective form of a UnitAssignment —
+captured at install time (photo + coords + maybe a free-text note),
+classified later (project + location chosen at a desk).
+
+Once classified, a real UnitAssignment is created, the pending row's
+status flips to "assigned", and resulting_assignment_id points at the
+new assignment for audit.
+
+Idempotent — safe to re-run.  Non-destructive — adds only.
+
+Run with:
+  docker exec terra-view-terra-view-1 python3 /app/backend/migrate_add_pending_deployments.py
+"""
+
+import os
+import sqlite3
+
+DB_PATH = "./data/seismo_fleet.db"
+
+
+def migrate_database() -> None:
+    if not os.path.exists(DB_PATH):
+        print(f"Database not found at {DB_PATH}")
+        return
+
+    conn = sqlite3.connect(DB_PATH)
+    cur  = conn.cursor()
+
+    cur.execute("""
+        CREATE TABLE IF NOT EXISTS pending_deployments (
+            id                       TEXT PRIMARY KEY,
+            unit_id                  TEXT NOT NULL,
+            captured_at              DATETIME NOT NULL,
+            coordinates              TEXT,
+            operator_note            TEXT,
+            photo_filename           TEXT,
+            status                   TEXT NOT NULL DEFAULT 'awaiting',
+            promoted_at              DATETIME,
+            resulting_assignment_id  TEXT,
+            cancelled_at             DATETIME,
+            cancelled_reason         TEXT,
+            created_at               DATETIME NOT NULL DEFAULT (datetime('now')),
+            updated_at               DATETIME NOT NULL DEFAULT (datetime('now'))
+        )
+    """)
+    print("  Table 'pending_deployments' ready.")
+
+    # Indexes — operators will query by status (hopper list) and by
+    # unit_id (per-unit detail page → "is there a pending capture?").
+    cur.execute("""
+        CREATE INDEX IF NOT EXISTS idx_pending_deployments_status
+            ON pending_deployments (status)
+    """)
+    cur.execute("""
+        CREATE INDEX IF NOT EXISTS idx_pending_deployments_unit_id
+            ON pending_deployments (unit_id)
+    """)
+    cur.execute("""
+        CREATE INDEX IF NOT EXISTS idx_pending_deployments_captured_at
+            ON pending_deployments (captured_at)
+    """)
+    print("  Indexes ready.")
+
+    conn.commit()
+    conn.close()
+
+
+if __name__ == "__main__":
+    print("Running migration: add pending_deployments table")
+    migrate_database()
+    print("Done.")