Fix --offline flag: it is parsed but currently a no-op #11

Summary

analyze accepts an --offline flag, but cmd/optiqor/main.go comments it as "always true in Phase 1" and never reads its value. This is confusing: users who pass --offline expect a guarantee that no network calls will be made, but they get no signal that the flag did anything.

Steps to reproduce

optiqor analyze ./my-chart --offline
# No error, but the flag has no observable effect or documented guarantee.

What to do

1. Locate the --offline binding in cmd/optiqor/main.go (near the analyze command flags).
2. Delete the "always true in Phase 1" comment and actually read the flag.
3. If --offline is set (or OPTIQOR_OFFLINE=1 env var), and --share is also set, print a warning:

   warning: --share is ignored in --offline mode
   

   and skip the upload without exiting non-zero.
4. Document the flag clearly in --help.

Acceptance criteria

• --offline --share prints a warning and skips the upload instead of silently uploading.
• OPTIQOR_OFFLINE=1 is honoured identically to --offline.
• The flag is documented in optiqor analyze --help.
• make lint test passes.

Why this is a good first issue

• Isolated change: only cmd/optiqor/main.go and the --share upload path in internal/share/share.go.
• Good entry point to understanding how flags flow through the CLI.