feat(sfm): strip "- Loc N" suffix from operator-typed project names

Operators sometimes bake location identifiers into the project string
for email-readability — "Fay - Locks & Dam No3 - Loc 2 - 735 Bunola"
where "Fay - Locks & Dam No3" is the actual project and "- Loc 2 -
735 Bunola" is location info that already lives in sensor_location.
Without stripping, every "- Loc N" variant became a separate project,
fragmenting what should be one project with several locations.

Backend:
- New _extract_project_root() helper.  Regex matches " - Loc N" / "-Loc3" /
  " - Location #5" / etc. with case-insensitive multi-dash support; strips
  from that marker forward and cleans up dangling separators.  Strings
  without a Loc-marker pass through unchanged.

- Cluster dataclass adds project_root field alongside project_raw.
  project_raw stays the operator-typed string for display ("hover to see
  what was actually typed").  project_root is what gets normalised for
  matching and used as the suggested project name.

- _ensure_project + _ensure_location now do normalisation-aware dedup
  before creating: a cluster of "SR81" and a cluster of "SR 81" (which
  normalise to the same string) collapse into one project on apply,
  even when applied in the same bulk operation.  Avoids UNIQUE
  constraint collisions and duplicate-named-by-spacing projects.

Frontend:
- Wizard cluster cards show "↳ stripped trailing 'Loc N' suffix; operator
  typed: <raw>" when project_root differs from project_raw, so the
  operator can see at a glance what the parser did to the string.

Real-data results: against the same 10,055 SFM events, confidence
distribution improved from 37/14/8 (high/med/low) to 43/9/7.  "Fay -
Locks & Dam No3" now appears as ONE project across 6 cluster instances
spanning 3 serials and 6 different locations — exactly the
"one project, many locations" model the user described.

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

backend/routers/metadata_backfill.py

@@ -46,6 +46,7 @@ def _serialise_suggestion(s: svc.Suggestion) -> dict:
         "event_count":             c.event_count,
         "sample_event_id":         c.sample_event_id,
         "project_raw":             c.project_raw,
+        "project_root":            c.project_root,
         "location_raw":            c.location_raw,
         "client_raw":              c.client_raw,
         "operator_raw":            c.operator_raw,