I10 (audit-I42+I50+I51+I57): missing/lying CLI surfaces

[espadonne]

Summary

Closes audit-I42 + I50 + I51 + I57 — every surface where the CLI either failed to dispatch through a working server endpoint, or advertised a flag the server doesn't honor.

What landed

• `repo list ` (audit-I42, CRIT) — pre-fix only hit `/users/{X}/repos` and bailed with "user not found" when X was an org. Now: try user first, fall back to `/orgs/{X}/repos` when the user lookup 404s. When both 404, the user-side NotFoundError propagates unchanged.
• `repo edit --archived / --unarchive` (audit-I50, MED) — typed flags for the archive bit. Server already honors `archived` on PATCH; the raw-API workaround (`api -X PATCH /repos/{O}/{R} -F archived=true`) wasn't discoverable. The two flags are mutually exclusive; pass either one.
• `repo edit --visibility internal` (audit-I51, CRIT) — server 422s "visibility must be public or private". Drop `internal` from the help text and validate client-side so the error names the actual flag instead of letting the API speak. Same lie removed from `repo create --internal` (flag removed, "Internal" stripped from the interactive prompt).
• `repo edit --enable-projects/--enable-wiki/--enable-discussions` (audit-I57, MIN) — the help already said "no-op on shithub for now" but the CLI still printed `✓ Updated` for a request that did nothing. Now prints a `note:` per passed vapor flag so the user knows the server has no behavior to attach.

Out of scope

• I43 (`org view --json publicRepos` always 0) — deferred from I8; needs a server-side `/api/v1/orgs/{org}` GET endpoint that doesn't exist yet. Tracked separately for a future I-N or J-pass.

Test plan

• Build + vet clean
• `TestListFallsBackToOrgOn404` + `TestListPropagatesUserNotFoundWhenOrgAlsoMisses` pin I42
• Full `./pkg/cmd/repo/...` test suite green
• Dogfood post-merge: `shithub repo list tenseleyflow` returns org repos; `shithub repo edit $REPO --archived` succeeds; `--visibility internal` rejects cleanly; `--enable-projects` prints note

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