feat: prepare GitHub App for Marketplace listing

LISTING.md

@@ -0,0 +1,86 @@
+# Marketplace listing copy kit
+
+Ready-to-paste copy for the GitHub Marketplace listing. Sections map to the fields
+in the Marketplace listing editor. Copy follows GitHub's style rules: sentence
+case, active voice, serial commas, and no trailing punctuation on titles.
+
+## Listing name
+
+```
+Signetry Admission
+```
+
+## Very short description
+
+Sentence case, describes functionality, no trailing punctuation, no call to action,
+does not repeat the app name. (66 characters.)
+
+```
+Governs coding-agent pull requests with a signed admission receipt
+```
+
+## Categories
+
+- **Primary:** Code review
+- **Secondary:** Code quality
+
+## Introductory description
+
+Begins with the app name, active voice, 150-250 characters. (160 characters.)
+
+```
+Signetry Admission reviews every coding-agent pull request and posts one advisory verdict with reasons and a signed receipt, so a human still decides the merge.
+```
+
+## Detailed description
+
+Under 1000 characters. Each value proposition is a level-3 header followed by a
+short paragraph. Sentence case, periods, no exclamation marks.
+
+```markdown
+### Earned authority, not blanket access
+
+Signetry Admission acts through a short-lived, read-only installation token scoped
+to the pull request under review. It posts one advisory comment and nothing more.
+
+### Injection-resistant by construction
+
+The review is comment-only and the app never runs your diff as an instruction. It
+reasons about the change, then reports, so prompt injection in a PR cannot escalate
+into an action.
+
+### Proof you can verify
+
+Every verdict links to a signed receipt. The comment restates the receipt and
+claims nothing beyond it, so anyone can check what was decided and why.
+
+### A human always merges
+
+Signetry Admission never merges and never enables auto-merge. It advises, and a
+person makes the final call on every pull request.
+```
+
+## Required URLs
+
+- **Customer support URL:** `https://github.com/Signetry/github-app/blob/main/SUPPORT.md`
+- **Privacy policy URL:** `https://github.com/Signetry/github-app/blob/main/PRIVACY.md`
+- **Homepage URL:** `https://signetry.github.io`
+- **Documentation URL:** `https://github.com/Signetry/signetry`
+
+## Pricing
+
+Use a **Free plan**. A free plan satisfies the Marketplace pricing requirement and
+keeps onboarding frictionless. The app already handles `marketplace_purchase`
+webhook events, so it is ready to react to purchases, cancellations, and plan
+changes if paid plans are added later.
+
+## Logo and feature card
+
+Both assets are prepared to GitHub's specs:
+
+- **Logo:** 200x200 px, transparent background.
+- **Feature card:** 965x482 px.
+
+Upload the logo under the app's settings (Developer settings → GitHub Apps → your
+app → Display information), and upload the feature card in the Marketplace listing
+editor under the listing's branding section.

PRIVACY.md

@@ -0,0 +1,63 @@
+# Privacy Policy
+
+_Last updated: 2026-08-12_
+
+This policy explains what data the Signetry GitHub App accesses, what it does with
+that data, and what it does not do. It is written to be honest and specific to how
+this app actually works: it performs comment-only admission review on pull requests
+and never merges them.
+
+## What the app accesses
+
+The app operates only on the accounts, organizations, and repositories where an
+owner has explicitly installed it, and only within the permissions granted at
+install time:
+
+- **Pull requests (read and write):** pull request metadata (title, author,
+  branch, state) and the ability to post advisory review comments.
+- **Contents (read-only):** the file contents and diff of a pull request under
+  review, so the admission review can reason about the proposed change.
+- **Metadata (read-only):** basic repository metadata GitHub exposes to all apps.
+
+The app subscribes to `pull_request`, `installation`, `installation_repositories`,
+and `marketplace_purchase` events. Installation events tell the app which
+repositories it covers. Marketplace events tell the app about purchases,
+cancellations, and plan changes for billing.
+
+## What the app does with it
+
+When a reviewable pull request is opened or updated, the app mints a short-lived
+installation token, reads the diff, runs an admission review, and posts **one
+advisory comment** containing a verdict, the reasons for it, and a link to a signed
+receipt. The comment restates the receipt and claims nothing beyond it.
+
+The app is **comment-only**. It never merges, never enables auto-merge, and never
+pushes code. A human always decides whether to merge.
+
+## What the app does not do
+
+- It does **not** store your code beyond the duration of a review. Diffs are read
+  to produce the review and are not retained as a durable copy afterward.
+- It does **not** sell, rent, or share your data with third parties for marketing
+  or advertising.
+- It does **not** pass its installation token to any coding-agent child process.
+
+## Model calls and bring-your-own-key
+
+Any calls to a language model use a **bring-your-own-key** model: the operator
+supplies their own model provider credentials. The app does not send your code to a
+model provider using Signetry-owned keys, and it does not use your data to train
+models.
+
+## Data retention
+
+The app retains only what it needs to operate the service: installation records
+(which repositories are covered), billing state derived from Marketplace events,
+and the signed receipts it issues. Pull request diffs are processed transiently for
+each review and are not kept as a durable copy.
+
+## Contact
+
+For privacy questions or concerns, or to report a data-handling issue, open a
+private security advisory on the [Signetry/github-app](https://github.com/Signetry/github-app/security/advisories)
+repository, or contact the Signetry organization through its GitHub profile.

SUPPORT.md

@@ -0,0 +1,28 @@
+# Support
+
+Thanks for using the Signetry GitHub App. Here is how to get help.
+
+## Report a bug or request a feature
+
+Open an issue on
+[Signetry/github-app](https://github.com/Signetry/github-app/issues). Include your
+GitHub App version or slug, the repository or installation affected, and the steps
+to reproduce the problem.
+
+## Ask a question or start a discussion
+
+Use the platform Discussions at
+[Signetry/signetry](https://github.com/Signetry/signetry/discussions) for
+questions, ideas, and general help that is not a specific bug.
+
+## Report a security issue
+
+Do not open a public issue for an unpatched vulnerability. Instead, use private
+vulnerability reporting by opening a security advisory on
+[Signetry/github-app](https://github.com/Signetry/github-app/security/advisories).
+See [SECURITY.md](SECURITY.md) for the full policy.
+
+## Response expectations
+
+This is a maintained project, but response times may vary. Security reports are
+prioritized over feature requests.

app-manifest.json

@@ -12,7 +12,8 @@
   "default_events": [
     "pull_request",
     "installation",
-    "installation_repositories"
+    "installation_repositories",
+    "marketplace_purchase"
   ],
   "default_permissions": {
     "pull_requests": "write",