parse PR URLs in args

[skarim]

Accept PR URLs as arguments in link and checkout

Currently, gh stack link and gh stack checkout only accept PR numbers (e.g. 42) or branch names as arguments. Users who copy-paste a PR URL from the GitHub UI (e.g. https://github.com/owner/repo/pull/42) get confusing behavior — the URL is interpreted as a branch name, which either fails silently or produces an unhelpful error.

A parsePRURL helper already existed in cmd/utils.go (used by switch, navigate, etc. for local stack resolution), but was not wired into link or checkout.

This change adds PR URL parsing to both commands so that gh stack link https://github.com/o/r/pull/41 https://github.com/o/r/pull/42 works the same as gh stack link 41 42, and gh stack checkout https://github.com/o/r/pull/42 works the same as gh stack checkout 42.

Changes

• cmd/link.go: in findExistingPR, add a parsePRURL check before the strconv.Atoi numeric path. If a URL is detected but the PR does not exist, error immediately (a URL can never be a valid branch name, so falling through to branch lookup would be wrong). Update command help text and examples.
• cmd/checkout.go: in runCheckout, add a parsePRURL check before the strconv.Atoi check. Route the extracted PR number to resolveNumericTarget, enabling both local lookup and remote API fallback — same behavior as passing a PR number directly. Update command help text and examples.
• cmd/link_test.go: 3 new tests — PR URLs creating a stack, URL for non-existent PR producing an error, mixed URLs and numbers
• cmd/checkout_test.go: 2 new tests — PR URL resolving against a local stack (no API), PR URL triggering remote stack import
• README.md, docs/src/content/docs/reference/cli.md, docs/src/content/docs/introduction/overview.md, docs/src/content/docs/faq.md: update documentation to mention PR URLs as accepted input

Closes #115

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[Copilot]

Pull request overview

This PR extends gh stack link and gh stack checkout to accept GitHub PR URLs (e.g., https://github.com/owner/repo/pull/42) in addition to PR numbers and branch names. It leverages the existing parsePRURL utility that was already used internally by other commands like switch and navigate, and wires it into the argument resolution logic of link and checkout.

Changes:

• Added PR URL parsing in findExistingPR (link) and runCheckout (checkout) that routes parsed URLs through the same resolution paths as numeric PR arguments
• Added 5 new tests covering URL-based stack creation, not-found errors, mixed input, and both local and remote checkout paths
• Updated documentation (README, CLI reference, overview) to reflect URL support

Show a summary per file

File	Description
cmd/link.go	Added parsePRURL check in findExistingPR before numeric parsing; errors immediately if URL-specified PR not found (URLs can never be branch names). Updated command help text and examples.
cmd/checkout.go	Added parsePRURL check in runCheckout before numeric parsing; routes extracted number to resolveNumericTarget for consistent local/remote resolution. Updated command help text and examples.
cmd/link_test.go	3 new tests: URL stack creation, URL not-found error, mixed URLs and numbers.
cmd/checkout_test.go	2 new tests: URL resolving against local stack (no API), URL triggering remote stack import.
README.md	Updated checkout and link sections to mention PR URLs with examples.
docs/src/content/docs/reference/cli.md	Mirror of README documentation updates for the docs site.
docs/src/content/docs/introduction/overview.md	Updated overview bullet to mention URL support for checkout.

Copilot's findings

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• Files reviewed: 7/7 changed files
• Comments generated: 0

[ktravers]

Nice quality of life improvement ✨

[Lukeghenco]

Nit: I know this is in the previous code too, but why does Long have a back tick but the Use and Short use double quotes " since there is no string interpolation here?

[skarim]

We use backticks for the Long descriptions because it's a multi-line text and raw string literals preserve the line breaks. I guess we could use backticks for all of the strings here, but I feel like using double quotes (interpreted string literal) is usually safer and a better default 🤷

[Lukeghenco]

🥳

[Lukeghenco]

I like the added utility this adds to the CLI. Looks good to 🚢.