fix(templates): explain a per-member connection instead of a bare checkbox

[pythonlearner1025]

From annotations on blitzos.com/templates/new. Covers items 1–4; the GitHub
App work (item 5) is deliberately not here.

The bug behind three of the four annotations

Google Workspace, Linear and YouTrack each rendered a checkbox and nothing
else when picked — no button, no note, no hint that the member signs in later
inside their workspace.

One gate causes all three. Every note and button in the connection block hangs
off:

const wantsOrgConfig = chosen !== null && entry.adminForm !== null;

and those three providers carry adminForm: null in the catalog
(google-workspace.ts:34, linear.ts:37, youtrack.ts:30), against
github.ts:39 and discord.ts:25 which do not. So the entire block was skipped
for exactly the providers that most needed a word of explanation.

They now render the sentence the org-key providers already use — "Members
sign in to X themselves." — rather than a second phrasing to keep in step.

The fourth annotation

The repo picker said "Set up GitHub above first" for what every other label on
the surface calls connecting. It now says "Connect GitHub above first".

Evidence

Both changes are pinned by tests that fail against the previous renderer:

× explains a per-member provider when it is picked, with no admin form
    expected … to contain 'Members sign in to YouTrack themselves.'
× lights up the repo picker when the admin saves the credential inline
    expected … to contain 'Connect GitHub above first'

The first is the existing per-member test, extended and renamed — its old name
promised only the absence of an admin form, which is no longer all it guards.
The second already existed and pinned the old string.

webapp vitest: 299 pass.

Not in this PR

Annotation 5 asks for a BlitzOS GitHub App: "Connect with BlitzOS app" beside
"Connect with my app", the latter replacing "Add GitHub key". That is an app
registration, an install callback, org and repo scoping, installation-token
minting, and a migration path for anyone already on a PAT. It needs decisions
before code and does not belong bolted onto a copy fix.

Not verified

No browser check — this sandbox has no local control plane. The assertions are
on rendered text through the real component, not on a screenshot.

🤖 Generated with Claude Code