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/git_push_if_ahead.md

@@ -0,0 +1,56 @@
+---
+name: git_push_if_ahead
+kind: function
+lang: bash
+domain: infra
+version: "1.0.0"
+purity: impure
+signature: "git_push_if_ahead(repo_dir: string) -> stdout: status line"
+description: "Decide si pushear un repo git usando solo refs locales (sin tocar la red para decidir). Sin upstream hace push -u; con upstream y ahead > 0 pushea; con 0 ahead salta. Si el push falla no aborta — emite [error] y exit 0."
+tags: [git, push, infra, ahead, upstream]
+uses_functions: []
+uses_types: []
+returns: []
+returns_optional: false
+error_type: "error_go_core"
+imports: []
+params:
+  - name: repo_dir
+    desc: "path al repo git a evaluar; default '.'"
+output: "linea de estado por stdout: '[push -u] repo (branch)', '[push] repo (branch, N commits ahead)', '[skip] repo (up-to-date)' o '[error] repo: razon'"
+tested: false
+tests: []
+test_file_path: ""
+file_path: "bash/functions/infra/git_push_if_ahead.sh"
+---
+
+## Ejemplo
+
+```bash
+source bash/functions/infra/git_push_if_ahead.sh
+
+# Pushear si hay commits locales
+status=$(git_push_if_ahead /home/lucas/fn_registry)
+echo "$status"
+# [push] fn_registry (master, 3 commits ahead)
+# o:
+# [skip] fn_registry (up-to-date)
+
+# Iterar sobre multiples repos
+while IFS= read -r repo; do
+    git_push_if_ahead "$repo"
+done < <(discover_git_repos /home/lucas/fn_registry)
+```
+
+## Estados de salida
+
+| Linea stdout | Significado |
+|---|---|
+| `[push -u] repo (branch)` | Sin upstream — se hizo push -u origin |
+| `[push] repo (branch, N ahead)` | Tenia commits locales — se pusheo |
+| `[skip] repo (up-to-date)` | 0 ahead localmente — no se toco la red |
+| `[error] repo: razon` | Push rechazo (non-fast-forward, etc.) — se reporta pero exit 0 |
+
+## Notas
+
+`rev-list --count @{u}..HEAD` solo lee refs locales, no hace fetch. Esto es correcto para un push-only workflow: si en otro PC se hizo push, aqui no tenemos nada local que pushear de todas formas. El error `[error]` tipicamente indica que la rama remote esta adelante — el caller debe sugerir `/full-git-pull`.