refactor(uv): single managed-uv path, delete fts5 installer escalation

Replace the multi-path UV resolution chain (PATH probing, conda guards,
5-location trust ordering, temp-dir fallback installs) with a single
managed uv binary at $HERMES_HOME/bin/uv. Every code path that needs
uv resolves it from that one location; if missing, ensure_uv()
bootstraps it via the official standalone installer.

Key changes:

- New hermes_cli/managed_uv.py: managed_uv_path(), resolve_uv(),
  ensure_uv() (returns (path, freshly_bootstrapped) tuple),
  update_managed_uv(), rebuild_venv(), installer internals.
- hermes_cli/main.py: replace all shutil.which('uv') with ensure_uv(),
  add venv rebuild on first-time managed uv bootstrap, update_managed_uv
  before dep install on all 3 update paths.
- scripts/install.sh: install_uv() always installs to
  $HERMES_HOME/bin/uv; delete ensure_fts5, _python_has_fts5,
  _reinstall_python_with_fts5, _warn_no_fts5 (61 lines).
  Managed uv always installs current Python with FTS5.
- scripts/install.ps1: Install-Uv always installs to
  $HermesHome\bin\uv.exe; Resolve-UvCmd checks managed location first.
- hermes_state.py: simplified FTS5 warning now suggests 'hermes update'
  as the fix instead of blaming install method.
- tests: 15 tests in test_managed_uv.py, autouse _patch_managed_uv
  fixture in test_cmd_update.py.

Closes #37605, Closes #37622

hermes_state.py

@@ -452,12 +452,9 @@ class SessionDB:
         self._fts_unavailable_warned = True
         logger.warning(
             "SQLite FTS5 unavailable for %s; full-text session search "
-            "disabled. This usually means Hermes is running on an "
-            "unsupported install (e.g. a pip-installed or pip-managed "
-            "Python whose bundled SQLite lacks FTS5) rather than a "
-            "mainline install. Some features may be missing or behave "
-            "differently. Install the supported way: "
-            "https://hermes-agent.nousresearch.com (underlying error: %s)",
+            "disabled. Run `hermes update` to rebuild the venv with a "
+            "current Python (managed uv guarantees FTS5). "
+            "(underlying error: %s)",
             self.db_path,
             exc,
         )