fix(watcher): report a tree-polled non-git root as strategy "tree"

Since #1948 a non-git root can be polled by a file-tree scan when
watch_non_git is on. index_status still reported such a root as
strategy "none", which the enum documents as "not a git project: never
polled", so a root that is actively polled looked unwatched.

publish_status now maps a tree-polled root to the new
CBM_WATCHER_STRATEGY_TREE, rendered as "tree" (the value the
watcher.baseline log already uses). "none" keeps its meaning: a
registered non-git root that is never polled. CONFIGURATION.md lists
the four values.

Test: daemon_application_index_status_reports_tree_strategy_issue2167
fails without the production change and passes with it; suites
daemon_application, watcher and mcp: 507 passed, 4 platform skips.

Signed-off-by: Martin Vogel <martin.vogel.tech@gmail.com>

docs/CONFIGURATION.md

@@ -93,6 +93,12 @@ Current keys:
 | `index_max_files` | `off` | Optional maximum number of accepted source files in one discovery run. |
 | `index_max_source_mb` | `off` | Optional maximum accepted source size in MiB in one discovery run. |
 
+For a watched project, `index_status` names the polling method in `watch.strategy`:
+`git` (HEAD and dirty-state polling), `tree` (a non-git root polled by the
+`watch_non_git` file-tree scan), `none` (a non-git root that is registered but never
+polled, the default for a plain directory) or `pending` (registered; the first poll
+has not run yet).
+
 > **`watcher_enabled` vs `auto_watch`.** `watcher_enabled` controls whether the
 > watcher *subsystem* starts at all (the background poll thread). `auto_watch` is
 > narrower: it only controls whether a connecting session registers *its own*