Add Tiny Tool Town submission canvas (#2240)

* Add Tiny Tool Town submission canvas

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Add generated description choices

Resolve picker opens from the active session working directory so linked worktrees work without an explicit repository path.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Address Tiny Tool review comments

Detect root .csproj files as build signals and hide canvas access tokens from the visible URL after first load.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Address latest Tiny Tool review comments

Handle root-relative README images, preserve drafts during refresh, and suppress GitHub mentions before public issue creation.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

* Address canvas shutdown and CSP review

Close all canvas servers during shutdown, use nonce-based CSP, make theme optional, and hide decorative preview dots from assistive tech.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

.github/plugin/marketplace.json

@@ -1062,6 +1062,12 @@
       "description": "Comprehensive collection for writing tests, test automation, and test-driven development including unit tests, integration tests, and end-to-end testing strategies.",
       "version": "1.0.0"
     },
+    {
+      "name": "tiny-tool-town-submitter",
+      "source": "extensions/tiny-tool-town-submitter",
+      "description": "Inspect a repository, improve Tiny Tool Town readiness, submit its listing issue, and launch remediation work.",
+      "version": "1.0.0"
+    },
     {
       "name": "token-pacman",
       "source": "extensions/token-pacman",