Convert PR numbers from plain text to clickable GitHub links using
rich_text cells with multiple link elements.

Changes:
- PR column now uses rich_text cell with link elements
- Each PR is a clickable link: #1234 → #1234
- Multiple PRs separated by commas: #1234, #1235
- Empty state remains plain text: "—"

Example table cell structure:
{
  "type": "rich_text",
  "elements": [{
    "type": "rich_text_section",
    "elements": [
      {"type": "link", "url": "https://...", "text": "#1234"},
      {"type": "text", "text": ", "},
      {"type": "link", "url": "https://...", "text": "#1235"}
    ]
  }]
}

Users can now click PR numbers directly in Slack tables to view
the pull requests on GitHub.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Replace separate "PRs Missing Jira" and "Issues with Missing Metadata"
sections with one unified "Release Contents" table showing everything.

Changes:
- New _create_all_pr_rows() function collects all PRs and issues
- All PRs shown in table (with or without Jira)
- All issues shown (complete and incomplete metadata)
- PRs without Jira show "No Jira" in Issue column
- Problems sorted first (incomplete), then by urgency
- Complete items shown after problems

Table structure:
- Urgency | Issue | fixVersion | affectedVersion | Priority | Severity | Deadline | PRs
- Shows ❌ for missing metadata, ✅ for present
- "No Jira" for PRs without Jira reference
- "—" for N/A fields

Benefits:
- Single comprehensive view of entire release
- Problems highlighted at top (sorted by completeness, then urgency)
- No separate sections to cross-reference
- Easy to see both what's good and what needs attention

Example rows:
- ❌ issue: ROX-123 | ❌ | ✅ | :jira-critical: | Important | Due: 2d | #1234
- ✅ issue: ROX-456 | ✅ | ✅ | :jira-major: | — | — | #1235
- No Jira PR: — | No Jira | — | — | — | — | — | #1236

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>