feat(v0.6-tail): close 5 v0.6-phase1-complete.md follow-ups

(1) Auto-call refresh-toggles on PUT /api/config/notifications
    meshai/dashboard/api/config_routes.py adds register_config_routes_hooks(app)
    which registers a FastAPI HTTP middleware: on any 2xx PUT whose path
    matches /api/config/notifications or /api/config, the middleware
    invokes _refresh_toggle_filter(app) which reaches into app.state.bus._
    pipeline_components["toggle_filter"] and calls .refresh(app.state.config).
    The dashboard no longer has to remember to ping POST /api/notifications/
    refresh-toggles after a toggle change. The explicit endpoint stays for
    backwards-compat.

(2) env_reporter block-size cap moved to adapter_config
    New registry row pipeline.env_reporter_block_chars (int, default 3000).
    meshai/notifications/env_reporter.py replaces the hardcoded
    _BLOCK_MAX_CHARS = 3000 with _DEFAULT_BLOCK_MAX_CHARS (the fallback) +
    a _block_cap() helper that reads from adapter_config on every slice.
    Mutating the row via PUT /api/adapter-config takes effect on the next
    env_reporter call -- no restart.

(3) Bulk-import endpoint for gauge_sites
    meshai/dashboard/api/gauge_sites_import.py adds
    POST /api/gauge-sites/import with two paths:
      format=csv      -- expects "data" (CSV text with header row matching
                          gauge_sites columns: site_id, gauge_name, lat, lon,
                          and optionally action_ft/flood_minor_ft/
                          flood_moderate_ft/flood_major_ft/enabled). UPSERT
                          via ON CONFLICT(site_id) DO UPDATE. Returns
                          {inserted, updated, skipped}.
      format=nws-ahps -- expects "wfo" (list of WFO codes). Fetches
                          water.weather.gov/ahps2/index.php?wfo=<WFO> for each,
                          regex-parses gauge links, then fetches up to 50
                          gauge detail pages per request and regex-parses
                          lat/lon + four threshold values. Best-effort; rows
                          stored under "AHPS-<gauge_id>" so they dont collide
                          with USGS-* ids. Returns the same shape plus
                          detail_fetched + errors list.
    Frontend (dashboard-frontend/src/pages/GaugeSites.tsx) gains a
    Import button + modal with two tabs (Paste CSV / Scrape NWS-AHPS)
    rendered via an ImportModal component. CSV tab has a 48-row textarea
    with the column-header hint inline; AHPS tab has a comma-separated WFO
    input defaulting to BOI. Both submit via fetch() and show the JSON
    response inline. Invalidates the curation cache server-side on any
    successful insert/update so nwis_handler sees the new gauges on its
    next call.

(4) WFIGS tombstone column -- CORRECTNESS
    v12.sql adds fires.tombstoned_at REAL (nullable) + idx_fires_tombstoned_at.
    meshai/central/wfigs_handler.py: the tombstone branch
    (kind=="wfigs_tombstone") UPDATE fires SET tombstoned_at=COALESCE(
    tombstoned_at, ?) so the first tombstone-time wins (idempotent against
    repeated tombstone envelopes).
    meshai/notifications/reminders/__init__.py: the wfigs tombstone
    termination condition now checks row["tombstoned_at"] IS NOT NULL.
    Reminders correctly STOP for closed fires -- before this change the
    8h cadence would have kept Active: broadcasts going indefinitely past
    a WFIGS removal.
    SCHEMA_VERSION 11 -> 12.

(5) Delete INCIDENT_BROADCAST_HEARTBEAT_S
    meshai/central/incident_handler.py: removed the dead constant
    (v0.5.9 REVISED dropped the heartbeat path but left the constant
    imported-but-never-read).
    tests/test_incident_handler.py: removed the orphan
    test_i_8h_heartbeat_triggers_update test (asserted None, used the
    deleted constant for time arithmetic) and the stray import line.

Tests (tests/test_tail_followups.py, 16 cases):
  - middleware fires refresh on PUT /api/config/notifications (200), does
    NOT fire on PUT /api/config/llm
  - env_reporter _block_cap() default 3000; mutate via PUT, invalidate,
    next read returns the new cap
  - CSV import inserts new rows, updates existing, skips bad rows,
    rejects missing required columns, rejects bad format
  - AHPS index parser extracts (gauge_id, name) from realistic HTML
  - AHPS detail parser extracts lat/lon + four thresholds from realistic
    HTML
  - fires has tombstoned_at column after migrations
  - wfigs tombstone branch stamps tombstoned_at
  - ReminderScheduler skips a fire whose tombstoned_at is NOT NULL
  - ReminderScheduler still fires for a fire whose tombstoned_at IS NULL
  - INCIDENT_BROADCAST_HEARTBEAT_S no longer importable

Foundation/API test counts bumped:
  REGISTRY 58 -> 59 (+ env_reporter_block_chars)
  schema_meta v11 -> v12

Test count: 844 -> 859 (+16 new, -1 deleted dead test). 0 regressions.

tests/test_adapter_config_foundation.py

@@ -54,11 +54,11 @@ def test_v6_tables_exist(fresh_db):
     assert "adapter_meta" in tables
 
 
-def test_schema_meta_at_v11(fresh_db):
+def test_schema_meta_at_v12(fresh_db):
     v = fresh_db.execute(
         "SELECT value FROM schema_meta WHERE key='version'"
     ).fetchone()["value"]
-    assert int(v) == 11
+    assert int(v) == 12
 
 
 def test_adapter_config_type_check_constrains_vocabulary(fresh_db):
@@ -73,9 +73,9 @@ def test_adapter_config_type_check_constrains_vocabulary(fresh_db):
 # ---------- registry shape -----------------------------------------------
 
 
-def test_registry_at_58_entries():
+def test_registry_at_59_entries():
     """v0.6-3a.1 trim: 43 CONFIG-only keys (was 77 in v0.6-3a draft)."""
-    assert len(REGISTRY) == 58, (
+    assert len(REGISTRY) == 59, (
         f"REGISTRY should have 43 entries after CONFIG-vs-CODE trim; got {len(REGISTRY)}. "
         f"If a sentence template / emoji / heuristic snuck in, it belongs in CODE not config."
     )