Add WACC builder skill to financial-analysis vertical

[HumphreySun98]

What

Adds a new wacc-builder skill under the financial-analysis vertical. It derives a defensible, fully auditable weighted-average cost of capital (WACC) as a standalone, reusable step that can feed the existing dcf-model, lbo-model, and comps-analysis skills.

Why

Today WACC is computed inline inside dcf-model. Pulling it into a dedicated skill adds:

• Reuse — one vetted discount rate shared across DCF, LBO, and comps, instead of re-deriving it per model.
• Auditability — a single cost-of-capital worksheet where every input carries a source and an as-of date.
• Rigor — an explicit peer-beta unlever → relever build for names whose own beta is noisy, newly listed, or capital-structure-distorted, plus optional size / country-risk premia and a deliberate target-vs-current structure choice.

What's in it

• A 6-step methodology: peer beta unlever/relever → CAPM cost of equity → after-tax cost of debt → market-value weights → WACC → ±0.5% sensitivity band.
• Follows repo conventions: MCP-first data-source priority, Correct Patterns / Common Mistakes sections, and the decision-support / human-sign-off guardrail (no investment recommendations).
• Hands off cleanly to dcf-model / lbo-model, and to xlsx-author for an Excel worksheet.

Validation

• python3 scripts/sync-agent-skills.py → clean.
• python3 scripts/check.py → OK — 80 file(s) checked, 0 issues.
• The pre-commit hook auto-bumped financial-analysis plugin.json 0.1.1 → 0.1.2.

Frontmatter is name + description only, matching existing vertical skills. The new skill is not bundled into any agent, so there is no sync drift and no manifest change beyond the automatic version bump.