Make the skills --verify catalog budget configurable

[cliffhall]

Follow-up from the review of #2293 (which closes #2248). See PR thread for this review comment.

Let's add this to the server settings. In a section called skills, add fields for Maximum number of skills (SKILL_MAX_CATALOG_SKILLS) and Maximum catalog size in bytes (SKILL_MAX_CATALOG_BYTES) populated by those values as defaults.

[cliffhall]

Triage: Priority Low (total 5)

• Severity 2 — minor friction: the catalog budget is hard-coded, and the workaround is editing the constant
• Urgency 2 — a follow-up from the feat: Skills extension phase 3 — CLI methods, TUI pane, resources/directory/read, and the frontmatter cross-check #2293 review; nothing waits on it
• Bonuses: +1 already milestoned (v2.7.0)

Board: #28, Status Todo (milestone already set; card was missing).

[cliffhall]

Shipped in #2367, merged into v2/main as 2f3099f. The skills verification catalog budget is now configurable per server:

• Where to set it: Server Settings → Skills (Maximum Number of Skills / Maximum Catalog Size), stored as skillCatalogMaxSkills / skillCatalogMaxBytes in mcp.json.
• Defaults: 256 skills / 64 MiB.
• Validation: both must be positive integers.
• Who reads it: the CLI's --verify and the TUI Skills pane.