docs(start): tighten login troubleshooting bullets for real user failure modes
Replace the generic five-bullet list with four Alex-oriented bullets
covering the concrete failure modes we actually see: Bluesky's "data is
invalid" page (browser session conflict), "Failed to resolve identity"
(DoH blocked, fall back to --app-password), CLI hang on a remote
machine (--remote), and DID-vs-handle guidance. Point to verbose mode
for cause chains.