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.sh

@@ -0,0 +1,83 @@
+#!/usr/bin/env bash
+# resolve_cpp_app_dir — Resuelve 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: usa el nombre directamente y busca en ambas ubicaciones.
+# Salida: "<app_name>\t<absolute_dir_path>" en stdout (TAB separado), exit 0.
+# Error: lista apps disponibles en stderr + exit 1.
+
+resolve_cpp_app_dir() {
+    local app_arg="${1:-}"
+    local root="${FN_REGISTRY_ROOT:-/home/lucas/fn_registry}"
+
+    # --- Deducir desde CWD si no hay argumento ---
+    if [ -z "$app_arg" ]; then
+        local cwd
+        cwd="$(pwd)"
+        case "$cwd" in
+            "$root"/cpp/apps/*/|"$root"/cpp/apps/*)
+                # Extraer primer segmento tras cpp/apps/
+                local rel="${cwd#"$root/cpp/apps/"}"
+                app_arg="${rel%%/*}"
+                ;;
+            "$root"/projects/*/apps/*/|"$root"/projects/*/apps/*)
+                # Extraer primer segmento tras la ultima /apps/
+                local rel="${cwd#"$root/projects/"}"
+                rel="${rel#*/apps/}"
+                app_arg="${rel%%/*}"
+                ;;
+        esac
+    fi
+
+    # --- Aun vacio: listar y abortar ---
+    if [ -z "$app_arg" ]; then
+        echo "ERROR: no se pudo deducir la app desde el directorio actual." >&2
+        echo "" >&2
+        echo "Apps disponibles:" >&2
+        {
+            ls "$root/cpp/apps/" 2>/dev/null | sed 's/^/  cpp\/apps\//'
+            for proj in "$root"/projects/*/apps/; do
+                ls "$proj" 2>/dev/null | sed "s|^|  $(echo "$proj" | sed "s|$root/||")|"
+            done
+        } >&2
+        echo "" >&2
+        echo "Uso: resolve_cpp_app_dir <app_name>" >&2
+        return 1
+    fi
+
+    # --- Buscar directorio real ---
+    local app_dir=""
+
+    # Primero: cpp/apps/<X>
+    if [ -d "$root/cpp/apps/$app_arg" ]; then
+        app_dir="$root/cpp/apps/$app_arg"
+    fi
+
+    # Segundo: projects/*/apps/<X> (primer match)
+    if [ -z "$app_dir" ]; then
+        for cand in "$root"/projects/*/apps/"$app_arg"; do
+            if [ -d "$cand" ]; then
+                app_dir="$cand"
+                break
+            fi
+        done
+    fi
+
+    if [ -z "$app_dir" ]; then
+        echo "ERROR: no se encuentra app '$app_arg' en cpp/apps/ ni en projects/*/apps/" >&2
+        echo "" >&2
+        echo "Apps disponibles:" >&2
+        {
+            ls "$root/cpp/apps/" 2>/dev/null | sed 's/^/  cpp\/apps\//'
+            for proj in "$root"/projects/*/apps/; do
+                ls "$proj" 2>/dev/null | sed "s|^|  $(echo "$proj" | sed "s|$root/||")|"
+            done
+        } >&2
+        return 1
+    fi
+
+    printf '%s\t%s\n' "$app_arg" "$app_dir"
+}
+
+if [ "${BASH_SOURCE[0]}" = "$0" ]; then
+    resolve_cpp_app_dir "$@"
+fi