Fix skeleton/validate/stats not finding plan-generated specs

[Dimwiddle]

Summary

Fixes #85 — specleft test skeleton, specleft features validate, and specleft features stats all reported "No specs found" after specleft plan successfully created spec files.

Root Cause

The parser (parser.py) required headings in strict # Feature: <title> format, but plan generates bare headings like # Document Lifecycle using the raw PRD heading text. Since the formats didn't match, all features were silently dropped.

Changes

• src/specleft/parser.py — Make SpecParser template-aware: new __init__ accepts an optional PRDTemplate, new _extract_feature_heading() tries each template pattern (most specific first) and falls back to raw heading text.
• src/specleft/schema.py — SpecsConfig.from_directory() now auto-resolves the PRD template from .specleft/templates/prd-template.yml and passes it to the parser.
• src/specleft/templates/prd_template.py — Added "{title}" catch-all to default feature and scenario pattern lists (last position, so more specific patterns are tried first).
• src/specleft/commands/init.py — Updated the init template content to match the new defaults.
• .specleft/templates/prd-template.yml — Updated project-local template with catch-all patterns.

Tests

• 6 new parser tests covering Feature: prefix, bare title, custom template, Feature without colon, template auto-loading, and fallback without template file.
• 2 new end-to-end skeleton tests verifying generation from plan-style bare headings.
• 1 updated test for new default pattern expectations.
• All 440 tests pass, lint clean.