Stop embedding the control token in every page (v0.9.10)

Closes TODO 2 of the security audit in docs/prs/2026-07-08-PR#000.

Every rendered page carried the live control token in a meta tag so that
gittally.js could send it, but no GET is authenticated — so `curl … |
grep gittally-control-token` handed the token to anyone, and read access
was effectively write access.

Reading stays fully public, which is a requirement rather than an
oversight: build states, logs and artifacts must be linkable from Gitea,
chats or tickets without a login. Only the distribution of the token
changed. The meta tag is gone; gittally.js keeps the token in
localStorage and asks for it once per browser, so knowing it requires
shell access to `.git/gittally/control-token` on the host. A token the
server rejects is dropped and asked for once more, so a rotated secret is
not a dead end. As a request header it stays inherently CSRF-safe.

The five branches of that flow (first use, reuse, stale token, cancelled
prompt, wrong token twice) were exercised against the real source with a
throwaway node harness; the UI test now asserts the token does not appear
in the rendered page. `docs/deployment.md` gained a "Control Token"
section on the public-read/token-protected-write split.

Co-Authored-By: Claude <noreply@anthropic.com>

build.gradle.kts

@@ -11,7 +11,7 @@ plugins {
 group = "de.hoennig"
 // bump at least the patch version for every deployment, so the UI footer
 // (BuildProperties) and --version identify what is actually running
-version = "0.9.9"
+version = "0.9.10"
 
 java {
     toolchain {