Add make roll-call for voluntary installation telemetry

[sebastientaggart]

Add a make roll-call Makefile target that lets users voluntarily post a check-in comment to a pinned GitHub Discussion (#133) on the CodeCannon repo. The command gathers repo name, CodeCannon version, and active adapters, shows a preview, asks for confirmation, then posts via the GraphQL API. No config changes, no skill changes — the opt-in is the act of running the command.

Issue #132

[sebastientaggart]

Review Summary

Verdict: APPROVE

Findings

No issues found. Code looks correct and follows project conventions.

Details reviewed:

• Preflight checks for gh installation and authentication are solid -- exits early with clear messages on failure.
• User confirmation prompt defaults to No ([y/N]), which is the safe default for a command that posts publicly.
• Privacy disclosure is explicit ("Your GitHub username and repo name will be visible").
• VERSION file lookup handles both CodeCannon/VERSION (submodule consumer) and VERSION (repo root) with an "unknown" fallback.
• The adapters variable defaults to "none detected" when .codecannon.yaml is missing or has no matches.
• The GraphQL mutation uses the hardcoded discussion node ID correctly with Make's $(...) syntax for the variable, and shell $$ escaping is correct throughout.
• .PHONY declaration updated to include roll-call.
• Help text updated with the new Community section.
• No secrets, no .env files, no sensitive data exposure.