Add Jenkins job trigger and improve CI link handling

[etnt]

• Add 'J' key binding to start a Jenkins PR pipeline build from the UI, with a confirmation dialog showing job name and branch details
• New py/jenkins.py module reads credentials from ~/.ghmanager_tokens (same as ghmanager) and triggers builds via Jenkins buildWithParameters API
• Auto-refresh PR after successful trigger to pick up new CI status
• Query dashboard API (dashboard.tail-f.com) for the latest build URL when pressing 'b', ensuring running builds are shown immediately
• Construct correct dashboard URL format with branch path and build ID
• Update help screen, CSS, config template, and README

[Copilot]

Pull request overview

Adds first-class Jenkins triggering and improves CI link freshness by integrating Jenkins build start and a dashboard API lookup into the prtui workflow.

Changes:

• Add J keybinding + modal confirmation to trigger a Jenkins PR pipeline build from the UI.
• Introduce py/jenkins.py to read ~/.ghmanager_tokens and trigger buildWithParameters via Jenkins API.
• Improve CI URL handling by querying dashboard.tail-f.com for the latest (including running) build URL.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
README.md	Documents Jenkins integration setup and usage.
py/prtui.tcss	Adds styling for the Jenkins confirmation modal.
py/prtui.py	Adds J binding, confirmation screen, Jenkins trigger workflow, and dashboard-based CI open behavior.
py/jenkins.py	New Jenkins client module: credential parsing, crumb fetch, and build trigger call.
py/ghapi.py	Adds dashboard CI URL lookup and prefers it when determining CI URL.

Comments suppressed due to low confidence (1)

py/prtui.py:630

• action_open_ci now performs a blocking HTTP request (ghapi.get_dashboard_ci_url(..., timeout=10)) on the UI thread. This can freeze the TUI while the request is in-flight or timing out. Consider moving the dashboard lookup into a background thread (similar to action_refresh_pr) and then opening the URL from call_from_thread, or rely on the already-stored ci_url from the last refresh when possible.

        table = self._focused_table()
        pr = self.prs.get(table.id or "", [])[table.cursor_row]
        # Try the dashboard API for the freshest build URL
        url = ghapi.get_dashboard_ci_url(pr.get("head_ref"))
        if not url:
            url = store.get_ci_url(repo, int(number))
        if not url:
            self.notify("No CI link found", severity="warning")
            return
        webbrowser.open(url)

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