docs(overview): enumerate dismissed_repair_count in fields= description

`dismissed_repair_count` is set on `ha_get_overview`'s response when the
caller omits `include_dismissed_repairs` (default) AND there are
dismissed repairs being hidden — it tells the agent how many were
filtered out so they know to flip the flag to see them. The key has
been emitted since #1309, but when #1225 introduced the comma-separated
``Available keys:`` enumeration in the `fields=` parameter description
the key was missed.

Functionally the key already worked via `fields=["dismissed_repair_count"]`
(project_fields passes it through), so this is a docstring/discoverability
fix — an agent reading the `fields=` description didn't know it could
request the key.

Adds a static regression test
(`tests/src/unit/test_fields_projection_docstring_completeness.py`) that
AST-walks the response builders for each tool with a `fields=` parameter
and asserts the `Available keys:` enumeration matches the keys the code
emits, in both directions:

  - emitted but not enumerated  — what slipped past on this PR's bug
  - enumerated but not assigned  — sibling drift in PR #1381 a473e16
    where `notifications`/`repairs` were documented but only assigned
    conditionally. Static AST catches "never assigned anywhere";
    "assigned only under `if x:`" needs runtime checking (which PR
    #1381's `TestHaGetOverviewAlwaysEmittedKeys` provides).

Covers 6 tools: ha_get_overview, ha_search_entities, ha_get_history,
ha_config_list_areas, ha_list_services (AST harvest), and ha_get_state
(manifest pin, since its keys come from HA's entity-record schema, not
from code we own).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: kingpanther13

src/ha_mcp/tools/tools_search.py

@@ -1230,8 +1230,9 @@ async def ha_get_overview(
                     "Available keys: success, system_summary, domain_stats, "
                     "area_analysis, ai_insights, pagination, partial, warnings, "
                     "device_types, service_availability, system_info, "
-                    "notification_count, notifications, repair_count, repairs, "
-                    "repairs_error, tool_discovery."
+                    "notification_count, notifications, repair_count, "
+                    "dismissed_repair_count, repairs, repairs_error, "
+                    "tool_discovery."
                 ),
             ),
         ] = None,