feat: implement phases 1-3 (config, content, data, cascade, permalink, collection, template, output, assets)

[zeroedin]

Summary

• Phase 1 (Config & Content): YAML/TOML/JSON config loading, front matter parsing, Goldmark markdown rendering with template tag preservation, lifecycle filtering (draft/publishDate/expiryDate), page bundle discovery
• Phase 2 (Data & Cascade): Data file loading (YAML/JSON/CSV), 5-level data cascade with deep merge and array replacement semantics
• Phase 3 (Permalink, Collection, Template, Output, Assets): Permalink token resolution with section-based lookup, collection building with date-based sorting, taxonomy system with slug collision detection, template context/filters/shortcodes/layout resolution, file output with pretty URLs/sitemap/feeds/formats, asset copying with hook processing

Test results

Package	Status
config	✅ pass
content	✅ pass
data	✅ pass
cascade	✅ pass
permalink	✅ pass
collection	✅ pass
template	⚠️ 108/120 pass (12 fail: GoEngine stub, liquid includes/compat — phases 4A/4B)
output	✅ pass
assets	✅ pass
cache	✅ pass
pagination	✅ pass
validation	✅ pass

Remaining failures are in unimplemented phases (4-7): liquid engine rewrite, Go template engine, static, pipeline, plugin, fetch, i18n, server, ssr, cmd, integration.

Test plan

• go test ./internal/config/... — all pass
• go test ./internal/content/... — all pass
• go test ./internal/data/... — all pass
• go test ./internal/cascade/... — all pass
• go test ./internal/permalink/... — all pass
• go test ./internal/collection/... — all pass
• go test ./internal/output/... — all pass
• go test ./internal/assets/... — all pass
• go vet ./... — clean

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