feat(TASK-048): install polish, hooks-dir mixin scan, script and probe hardening

- one shared exec-bit predicate (Language-recognized extensions => 0755) used by
  every hook/agent installer; non-script files in hooks dirs stay non-executable
- mixin discovery scans the global hooks dir and each agent's hooks dir;
  .builtin-manifest is never scanned
- NTFS 8.3 short-name aliases rejected as builtin-manifest entries
- hook-script install announcements restricted to real hook locations
- COYOTE_HOOKS_DIR override warning compares canonicalized paths
- embedded assets decode via checked from_utf8 instead of from_utf8_unchecked
- log-events.sh defaults under ${XDG_STATE_HOME:-$HOME/.local/state}/coyote/hooks.log
  keeping 0600/symlink-refusal/secret-filter hardening; notify.sh tty fallback strips
  control bytes; both use UTC ISO-8601 timestamps
- payload files orphaned by a write failure are unlinked; stale coyote-hook-*.json
  payloads swept best-effort at startup
- sweep_removed_agent_hooks never follows symlinked agent dirs
- usage-probe-hooks.sh replaces bare sleeps with a bounded poll, re-verifies 0755 on
  restored scripts, and covers roles/agent hook locations
- TestConfigDirGuard hoisted into crate::testing
- .gitattributes pins LF line endings for bundled scripts

hooks is now a reserved bundle name.

.gitattributes

@@ -1 +1,5 @@
 assets/config-template.yaml text eol=lf
+assets/hooks/*.sh text eol=lf
+assets/functions/tools/* text eol=lf
+assets/functions/scripts/* text eol=lf
+assets/functions/utils/*.sh text eol=lf