Point sparkle:releaseNotesLink at the landing /release-notes/{tag} route

[FuJacob]

Summary

Replaces the hard-coded GitHub release-tag URL inside scripts/generate_appcast.py with a configurable --release-notes-base-url flag (default https://cotabby.app/release-notes). Sparkle's WKWebView will now load a slim self-contained HTML page sized for its alert window instead of GitHub's full release page chrome.

Coordinates with the landing-site PR FuJacob/tabby-landing#2 which adds the /release-notes/[tag] Route Handler that serves that page.

Validation

python3 -c "import py_compile; py_compile.compile('scripts/generate_appcast.py', doraise=True)"
# syntax: OK

python3 scripts/generate_appcast.py --help
# new --release-notes-base-url flag appears with the documented default

python3 -c "import yaml; yaml.safe_load(open('.github/workflows/release.yml'))"
# release.yml: valid YAML

# Manual render smoke test (mocking the sign step):
#   release_page_url -> https://cotabby.app/release-notes/v1.6.0
#   <sparkle:releaseNotesLink>https://cotabby.app/release-notes/v1.6.0</sparkle:releaseNotesLink>

This PR deliberately does not cut a release tag. The change goes live when someone publishes the next tag.

Linked issues

Companion: FuJacob/tabby-landing#2 (landing Route Handler)

Risk / rollout notes

• Landing PR must deploy first. If this lands and a release tag is cut before the landing PR is live on https://cotabby.app/release-notes/[tag], Sparkle will fetch a 404 for the duration. Order: land + deploy landing, smoke-test the URL in a normal browser, then land this PR.
• Already-shipped builds are unaffected. Their appcasts are static XML files frozen at the time of their release; only future appcasts see the new URL.
• The base URL is exposed as a CLI flag rather than a constant so future environments (staging, fork, vendor mirror) can override without editing the script.
• Trailing slash on the base URL is normalized via rstrip("/"), so both https://cotabby.app/release-notes and https://cotabby.app/release-notes/ work.
• No Swift / Info.plist / Sparkle SDK changes. AppUpdateManager, signing pipeline, and appcast hosting all untouched.

Greptile Summary

This PR redirects Sparkle's sparkle:releaseNotesLink from the GitHub release page to a dedicated slim HTML route on the cotabby.app landing site, making the update alert's embedded WKWebView render a page sized for the small alert window rather than GitHub's full page chrome.

• scripts/generate_appcast.py: Adds DEFAULT_RELEASE_NOTES_BASE_URL constant and a --release-notes-base-url CLI flag; release_page_url is now assembled from this base + the release tag, with rstrip("/") normalization to handle trailing slashes.
• .github/workflows/release.yml: No flag is passed to the script (relying on the default), with an inline comment documenting the intentional omission and explaining when the override should be used.

Confidence Score: 5/5

Safe to merge once the companion landing-site PR is deployed; the script change itself is correct and self-contained.

The change is small and focused: it replaces one hard-coded GitHub URL with a configurable constant, adds trailing-slash normalization, and documents the intentional omission of the flag in CI. The previous review concern about duplicate URL values has been addressed by removing the flag from the workflow entirely. No logic errors, schema changes, or security implications were found.

No files require special attention. The deployment-ordering risk (landing site must go live before the next release tag is cut) is documented in the PR description rather than in code.

Important Files Changed

Filename	Overview
scripts/generate_appcast.py	Adds DEFAULT_RELEASE_NOTES_BASE_URL constant and --release-notes-base-url CLI flag; correctly assembles the release notes URL with trailing-slash normalization. No logic issues found.
.github/workflows/release.yml	Adds a comment explaining that --release-notes-base-url is intentionally omitted so the script's constant stays the single source of truth. Addresses the previous review concern cleanly.

Sequence Diagram

sequenceDiagram
    participant CI as GitHub Actions
    participant Script as generate_appcast.py
    participant XML as appcast.xml
    participant Sparkle as Sparkle (WKWebView)
    participant Landing as cotabby.app/release-notes

    CI->>Script: python3 generate_appcast.py (no --release-notes-base-url flag)
    Script->>Script: "release_notes_base = DEFAULT_RELEASE_NOTES_BASE_URL.rstrip("/")"
    Script->>Script: "release_page_url = "{base}/v{release_version}""
    Script->>XML: "render appcast.xml with sparkle:releaseNotesLink = https://cotabby.app/release-notes/vX.Y.Z"
    XML-->>CI: build/appcast.xml uploaded

    Note over Sparkle,Landing: At update-check time
    Sparkle->>Landing: GET /release-notes/vX.Y.Z
    Landing-->>Sparkle: Slim self-contained HTML page

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_{Reviews (2): Last reviewed commit: "Merge main; drop redundant --release-not..." | Re-trigger Greptile}