feat(doctor): add fn doctor CLI + 14 functions for system management

Adds `fn doctor` read-only diagnostic command with subcommands artefacts,
services, sync, uses-functions, unused, and --json flag for agents.
Each subcommand wraps a registry function in functions/infra/.

New functions:
- artefact_doctor, services_status, pc_locations_drift,
  audit_uses_functions, find_unused_functions (Go diagnostics)
- backup_sqlite_db, rotate_backups, wait_for_http, wait_for_port,
  port_kill, tail_journal, pre_commit_hook_install (bash utilities)
- notify_telegram (Go HTTP)
- backup_all pipeline (tag launcher)

Plus prior session leftovers (scan_secrets_in_dirty, append_diary_entry,
git utilities, http_session_cookie_middleware, compile/full-git pipelines).

Fixes pc_locations_drift filepath.Join bug with absolute dir_path.
Documents fn doctor in CLAUDE.md, .claude/rules/fn_doctor.md (rule 23),
docs/architecture.md, CHANGELOG.md (2026-05-07), and diary entry.

First fn doctor uses-functions run found drift in 7/12 apps (deuda
para sincronizar app.md con imports reales).

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

bash/functions/infra/discover_git_repos.md

@@ -0,0 +1,46 @@
+---
+name: discover_git_repos
+kind: function
+lang: bash
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "discover_git_repos(root_dir: string) -> stdout: newline-separated paths"
+description: "Encuentra todos los repos git dentro de root_dir. Devuelve paths absolutos (sin /.git) en stdout, uno por linea, ordenados. Incluye el propio root_dir si tiene .git. Excluye node_modules, .venv, cpp/vendor, cpp/build, sources, temp, subrepos e interior de .git."
+tags: [git, repo, discover, find, infra]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: []
+params:
+  - name: root_dir
+    desc: "directorio raiz a escanear (absoluto o relativo); default '.'"
+output: "paths absolutos newline-separated por stdout, uno por linea, ordenados alfabeticamente; el propio root_dir aparece primero si tiene .git"
+tested: false
+tests: []
+test_file_path: ""
+file_path: "bash/functions/infra/discover_git_repos.sh"
+---
+
+## Ejemplo
+
+```bash
+source bash/functions/infra/discover_git_repos.sh
+
+# Listar todos los repos bajo fn_registry
+discover_git_repos /home/lucas/fn_registry
+
+# Contar repos
+discover_git_repos /home/lucas/fn_registry | wc -l
+
+# Iterar
+while IFS= read -r repo; do
+    echo "Repo: $repo"
+done < <(discover_git_repos /home/lucas/fn_registry)
+```
+
+## Notas
+
+Usa `find` con `-mindepth 2` para subdirectorios (el root se comprueba por separado). Los resultados se emiten ordenados alfabeticamente. La funcion es impura porque lee el sistema de archivos. Sale con exit code 1 si `root_dir` no existe.