S001: support fuzzy section name matching

[hermanngeorge15]

Problem

S001 requires exact heading text match for required sections. The CLAUDE.md for this project has ## Acceptance Criteria — spec-linter v0.0.1 which fails because of the suffix.

Real-world spec files frequently append context to section names:

• ## Acceptance Criteria — v0.0.1
• ## Project Overview (Draft)
• ## Constraints / Phase 1

Proposal

Match required sections using startsWith or includes instead of exact match. For example, any heading that starts with "Acceptance Criteria" (case-insensitive) should satisfy S001.

Acceptance Criteria

• ## Acceptance Criteria — v0.0.1 passes S001
• ## Project Overview (Draft) passes S001
• Exact matches still work
• Tests updated

Labels

enhancement, rule:S001