refactor(backend): sanitize user input before logging to close CRLF injection (#807)

* refactor(backend): sanitize user input before logging to close CRLF injection

Adds a small sanitizeForLog helper that strips CR, LF, tab, and ASCII
control characters (0x00-0x1F, 0x7F) from a value before it is embedded
in a console.log/warn/error/debug call. Wraps every call site where a
user-controlled value (req.params, req.body, req.query, or a value
derived from them) flows into a log message.

Closes the bulk of the open CodeQL alerts in this family:
- 96 js/log-injection
- 28 js/tainted-format-string

The helper is in backend/src/utils/safeLog.ts. Routes still pre-validate
input at the request boundary; this is the second line of defense and
gives static analyzers a sanitizer they can trace through. JSON
responses, Docker filter labels, and other non-log call sites are
intentionally left unwrapped.

* refactor(backend): printf-style format strings for tainted-log call sites

CodeQL's js/tainted-format-string rule flags template literals in the first
arg of console.X when any interpolated value is user-controlled, regardless
of whether each value is sanitized inline. The canonical mitigation is to
use a static format string and pass values as positional args.

Converts the 28 flagged template literals to printf-style ("%s") format
strings, with sanitizeForLog applied to each positional arg. Also fills in
the log-injection wraps on 9 sites where a user-controlled value was
missed in the first sweep (agents, fleet, gitSources, imageUpdates,
GitSourceService).

No behavior change at runtime. Node's util.format substitutes %s tokens
identically to template-literal interpolation.

* fix(backend): wrap nodeId/snapshotId in fleet restore debug log

CodeQL flagged the unwrapped numeric args even though they cannot
contain control chars in practice. Apply the sanitizer for taint-flow
recognition.

backend/src/middleware/authGate.ts

@@ -2,6 +2,7 @@ import type { Request, Response, NextFunction, RequestHandler } from 'express';
 import { DatabaseService } from '../services/DatabaseService';
 import { isDebugEnabled } from '../utils/debug';
 import { getAuditSummary } from '../utils/audit-summaries';
+import { sanitizeForLog } from '../utils/safeLog';
 import { WEBHOOK_TRIGGER_RE } from '../helpers/routePatterns';
 import { authMiddleware } from './auth';
 
@@ -40,7 +41,7 @@ export const auditLog: RequestHandler = (req: Request, res: Response, next: Next
   res.on('finish', () => {
     try {
       if (isDebugEnabled()) {
-        console.log(`[Audit:diag] ${req.method} /api${apiPath} by=${username} status=${res.statusCode} node=${nodeId ?? 'local'} ip=${ip}`);
+        console.log(`[Audit:diag] ${sanitizeForLog(req.method)} /api${sanitizeForLog(apiPath)} by=${sanitizeForLog(username)} status=${res.statusCode} node=${nodeId ?? 'local'} ip=${sanitizeForLog(ip)}`);
       }
       DatabaseService.getInstance().insertAuditLog({
         timestamp: Date.now(),