Windsurf + Aider targets, MCP server, and demo placement (#33)

Broadens both reach (more tools) and content types (an MCP server), continuing
the multi-platform story.

Windsurf + Aider:
- build-exports.mjs gains two platforms: exports/windsurf/*.md (workspace rules,
  trigger: model_decision) and exports/aider/*.md (conventions for `aider --read`).
  Now 5 platforms (ChatGPT, Gemini, Cursor, Windsurf, Aider).
- install.sh + bin/cli.mjs install both (windsurf -> .windsurf/rules, aider ->
  .aider/skills with a --read hint); generated README index is excluded from copies.
- One-line windsurf-install.sh / aider-install.sh wrappers for parity.

MCP server (new content type):
- mcp/server.mjs — zero-dependency stdio MCP server exposing list_skills,
  search_skills, get_skill. Published as a second bin (pm-claude-skills-mcp).
  Logs to stderr; reads bundled skills/ at startup. mcp/README.md documents
  client config.

Also: README hero "See it in action" demo placement (ready to swap in a GIF;
recording guide in web/docs-assets/README.md), Works-With table + exports +
install docs updated, CHANGELOG Unreleased. package.json files/bin updated.


Claude-Session: https://claude.ai/code/session_016JWn5jRD5tcEFKrubjQ6Px

Co-authored-by: Claude <noreply@anthropic.com>

exports/aider/pm-finance/budget-variance-analysis/budget-variance-analysis.md

@@ -0,0 +1,62 @@
+# Budget Variance Analysis Skill
+
+Produces a complete variance analysis from numbers through to root cause explanation and management commentary.
+
+## Required Inputs
+- **Actuals and budget figures** (paste as table or describe line by line)
+- **Period** (month / quarter / YTD)
+- **Materiality threshold** (e.g. £10k or 5%)
+- **Known reasons for variances** (if any)
+- **Audience** (CFO / board / management / auditor)
+
+## Output Structure
+
+### 1. Variance Summary Table
+
+| Line Item | Budget | Actual | Variance £ | Variance % | F/A |
+|---|---|---|---|---|---|
+| Revenue | | | | | |
+| Cost of Sales | | | | | |
+| Gross Profit | | | | | |
+| Opex | | | | | |
+| EBITDA | | | | | |
+
+F = Favourable | A = Adverse
+
+### 2. Material Variance Commentary
+
+For each variance above threshold:
+
+**[Line item] — £[amount] F/A ([%])**
+- **Root cause:** [Specific explanation — not "timing" without detail]
+- **Permanent or timing?** Will this reverse next period?
+- **Management action:** What is being done
+- **Forecast impact:** Does this change full-year outlook?
+
+### 3. Top 3 Variances Requiring Attention
+Ranked by materiality and strategic significance.
+
+### 4. Forecast Revision
+Does the full-year forecast need updating? State revised expectation and key assumptions.
+
+### 5. Executive Summary
+3-4 sentences of management commentary suitable for a board pack.
+
+## Quality Checks
+- [ ] All variances above threshold explained
+- [ ] Root causes specific (not vague)
+- [ ] Favourable/Adverse correctly labelled
+- [ ] Forecast impact stated for material variances
+
+## Anti-Patterns
+
+- [ ] Do not explain a variance as "timing" without specifying which period it will reverse into and what amount is expected
+- [ ] Do not label a favourable variance on a cost line without checking whether it is due to underspend, delayed spend, or reduced activity — the cause determines whether it is genuinely good news
+- [ ] Do not omit variances below the materiality threshold entirely — note them collectively so the reader knows they exist and were reviewed
+- [ ] Do not present a variance analysis without a forecast impact statement for material items — historical variances without forward implications are incomplete
+
+## Example Trigger Phrases
+- "Write a variance analysis for these actuals vs budget: [paste]"
+- "Explain why we are over budget on [cost line]"
+- "Write the variance commentary for our finance review"
+- "Produce a budget vs actual analysis for Q[N]"