fix: replace empty catch blocks with meaningful error handling

[iamfj]

Problem

12 locations across the codebase use empty catch {} blocks that silently swallow errors. The most critical case is in token-storage.ts:

// src/common/token-storage.ts:41
try {
    const encrypted = fs.readFileSync(tokenPath, "utf8").trim();
    return decryptToken(encrypted);
} catch {
    return null; // corrupted token → user sees "No API token found"
}

A user with a corrupted token file gets "No API token found" instead of "Your stored token is corrupted" — sending them on a debugging wild goose chase.

All locations

File	Line	Impact
src/common/token-storage.ts	42	High — corrupted token invisible to user
src/commands/auth.ts	136, 142, 213, 229, 257	Medium — various auth flow fallbacks
src/services/file-service.ts	179, 262	Medium — file access/stat errors lost
src/common/identifier.ts	38	Low — intentional try-parse pattern
src/common/embed-parser.ts	62, 71	Low — URL parse fallback
src/commands/documents.ts	68	Low — URL parse fallback

Expected behavior

• token-storage.ts: Distinguish between "file not found" (return null) and "decryption failed" (log warning to stderr, return null)
• auth.ts: At minimum, add inline comments explaining what errors are expected
• file-service.ts: Surface the underlying error message in the result
• Low-impact locations: Add a comment explaining the intentional swallow, or narrow the catch to expected error types

Acceptance criteria

• No empty catch {} blocks remain without either error handling or an explanatory comment
• token-storage.ts prints a warning to stderr when decryption fails
• All existing tests still pass