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/resolve_cpp_app_dir.md

@@ -0,0 +1,47 @@
+---
+name: resolve_cpp_app_dir
+kind: function
+lang: bash
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "resolve_cpp_app_dir(app_name?: string) -> stdout: app_name\tapp_dir"
+description: "Resuelve el nombre y directorio absoluto de una app C++ del registry. Sin arg deduce desde CWD si esta dentro de cpp/apps/<X>/ o projects/*/apps/<X>/. Con arg busca en ambas ubicaciones. Imprime '<app_name>TAB<absolute_dir>' en stdout, exit 0; si no resuelve, lista apps disponibles en stderr y sale con exit 1."
+tags: [cpp, resolve, app, directory, infra]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: []
+tested: false
+tests: []
+test_file_path: ""
+file_path: "bash/functions/infra/resolve_cpp_app_dir.sh"
+params:
+  - name: app_name
+    desc: "Nombre de la app C++ a resolver (opcional). Sin arg se deduce desde el directorio actual si estamos dentro de cpp/apps/<X>/ o projects/*/apps/<X>/."
+output: "Una linea TAB-separada '<app_name>\\t<absolute_dir_path>' en stdout. En caso de error imprime ayuda a stderr y sale con exit 1."
+---
+
+## Ejemplo
+
+```bash
+# Desde dentro de cpp/apps/chart_demo/
+cd /home/lucas/fn_registry/cpp/apps/chart_demo
+resolve_cpp_app_dir
+# -> chart_demo\t/home/lucas/fn_registry/cpp/apps/chart_demo
+
+# Con argumento explicito
+resolve_cpp_app_dir registry_dashboard
+# -> registry_dashboard\t/home/lucas/fn_registry/cpp/apps/registry_dashboard
+
+# Capturar los dos campos
+resolved=$(resolve_cpp_app_dir graph_explorer)
+APP="$(echo "$resolved" | cut -f1)"
+APP_DIR="$(echo "$resolved" | cut -f2)"
+```
+
+## Notas
+
+Busca en orden: primero `$ROOT/cpp/apps/<X>`, luego `$ROOT/projects/*/apps/<X>` (primer match gana). Si ninguna ruta existe, imprime lista de apps disponibles (con prefijo de ubicacion) en stderr y sale con exit 1. Sourceable o ejecutable directamente.