Update label names and behavior

[claudiaregio]

Changed "fixed" label to "stable" label. We are now going to use "fixed" for when we validate. When a user comments "Status: Fixed" issue should get "fixed" label. When user comments "Status: Not Fixed", issue should get "not-fixed" label.

Also didn't want to make a separate branch to ship the calendar view-related skills for updating the iteration calendar view.

[emaf]

The two new skill files (docs/skills/calendar-view.md and docs/skills/canvas.md) have format issues that will prevent them from being discovered and loaded by agents.

Issues:

1. Wrong location — Skills must live under .github/skills/<name>/, .agents/skills/<name>/, or .claude/skills/<name>/. Placing them in docs/skills/ means agents won't recognize them as skills at all.

2. Wrong file name — The entry point for each skill must be named SKILL.md (not calendar-view.md or canvas.md).

3. Missing YAML frontmatter — Each SKILL.md requires a frontmatter block with at minimum name and description. The description is the discovery surface agents use to decide when to load the skill.

Suggested structure:

.github/skills/calendar-view/SKILL.md
.github/skills/canvas/SKILL.md

Suggested frontmatter for calendar-view:

---
name: calendar-view
description: 'Generate an interactive, scrollable HTML calendar view from a markdown schedule file. Use when someone provides a schedule with named events/dates and asks for a calendar view, visual timeline, or schedule visualization.'
---

Suggested frontmatter for canvas:

---
name: canvas
description: 'Show things visually using Canvas. Use when the human says "put this on the canvas," "show me a visual," "make a slide," or "visualize this." Canvas creates an HTML file and opens it as a borderless app window.'
---

The body content of both files looks great — just needs to be moved into the right structure with frontmatter added.

[emaf]

One question on validation-status-comment-label-handler.yml: the workflow only adds labels, so if a customer comments "Status: Fixed" and later "Status: Not Fixed" (or vice versa), the issue ends up with both fixed and not-fixed at the same time.

Two things worth thinking through:

• Should adding one status label automatically remove the other conflicting one?
• What's the intended behavior when you get mixed responses from multiple customers — e.g., some say fixed, some say not fixed? Is last-comment-wins the right policy, or should there be a way to reflect that the fix is working for some but not others?