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>

go.mod

@@ -12,6 +12,7 @@ require (
 	github.com/marcboeker/go-duckdb v1.8.5
 	github.com/mattn/go-sqlite3 v1.14.37
 	golang.org/x/crypto v0.50.0
+	golang.org/x/net v0.53.0
 	golang.org/x/sync v0.20.0
 	gopkg.in/yaml.v3 v3.0.1
 	nhooyr.io/websocket v1.8.17
@@ -62,7 +63,6 @@ require (
 	go.yaml.in/yaml/v3 v3.0.4 // indirect
 	golang.org/x/exp v0.0.0-20250128182459-e0ece0dbea4c // indirect
 	golang.org/x/mod v0.34.0 // indirect
-	golang.org/x/net v0.53.0 // indirect
 	golang.org/x/sys v0.43.0 // indirect
 	golang.org/x/telemetry v0.0.0-20260311193753-579e4da9a98c // indirect
 	golang.org/x/text v0.36.0 // indirect