chore: c6 docs-hygiene from cumulative_review_batches_28-30

Land F1+F2+F3 from the PASS_WITH_WARNINGS cumulative review of
batches 28-30 (AZ-305 / AZ-307 / AZ-308) before continuing to
batch 31. All three are bounded by the c6_tile_cache component;
no public API contract change beyond the new error re-export.

F1 (Medium / Architecture):
  Re-export CacheBudgetExhaustedError from c6_tile_cache package
  __init__ so consumers can catch the AZ-308 budget-exhaustion
  variant without widening to TileCacheError (which drops the
  needed_bytes / available_bytes / evicted_count diagnostics).

F2 (Medium / Architecture):
  Refresh the c6_tile_cache section of module-layout.md so the
  Public API line and the Internal-files list reflect what is
  actually on disk after batches 28-30 (drop the stale
  Tile / TileRecord / connection.py entries; add the AZ-305
  postgres_filesystem_store + tools.py, AZ-307 freshness_gate,
  AZ-308 cache_budget_enforcer entries; pivot the Public API
  bullet to the __init__.__all__ as canonical, mirroring the
  c7_inference section format).

F3 (Low / Maintainability):
  Promote the triplicate intra-module _iso_ts_now() helper into
  a single c6_tile_cache._timestamp.iso_ts_now and import it
  from postgres_filesystem_store, freshness_gate, and
  cache_budget_enforcer. FDR record envelope ts format now has
  one source of truth.

Test impact:
  tests/unit/c6_tile_cache: 105 passed, 57 skipped (pre-existing
  Docker-compose skip markers). No new tests required for F1/F2
  (re-export + doc) and F3 (pure refactor; existing tests assert
  FDR record shape, not the helper symbol).

Autodev state advanced to awaiting-invocation; next session
resumes greenfield Step 7 at batch 31 (AZ-298 TensorrtRuntime).

Co-authored-by: Cursor <cursoragent@cursor.com>

_docs/_autodev_state.md

@@ -6,9 +6,9 @@ step: 7
 name: Implement
 status: in_progress
 sub_step:
-  phase: 14
-  name: batch-loop
-  detail: "next: docs-hygiene mini-batch (F1+F2+F3 of cumulative_review_batches_28-30)"
+  phase: 0
+  name: awaiting-invocation
+  detail: "next batch 31: AZ-298 TensorrtRuntime"
 retry_count: 0
 cycle: 1
 tracker: jira