feat(wrap): oliver wrap template dialect (Phase 6 S2)

[drawmeanelephant]

Summary

Implements the oliver wrap subcommand with the 7-token template dialect (Phase 6 S2, issue #108).

What's new

• src/wrap.zig — Template dialect engine (filesystem-free, pure bytes → bytes)

  • 7 tokens: $title$/$description$/$author$/$date$/$palette$ (HTML-escaped), $assets_root$/$body$ (literal)
  • $if(name)$...$endif$ conditional blocks: first $endif$ closes, no nesting, verbatim unknown names, empty fields remove block
  • HTML escaping: & < > " ' → & < > " ' (matches GAWK html_escape)
  • JSON parsing via std.json.parseFromSlice with ignore_unknown_fields
  • 28 unit tests

• src/main.zig — CLI integration

  • New Command.wrap variant and 4 wrap-specific flags (--template, --meta-json, --assets-root, --body)
  • wrapDispatch() reads files from disk via std.Io.Dir.cwd().openFile(), resolves dialect, writes to stdout
  • Updated usage text and flag-scoping validation

CLI

oliver wrap --template <file> --meta-json <json> --assets-root <prefix> --body <file> > page.html

Contract

Matches oliver-contract.md:115-145:

• 7 tokens with correct escaping split
• $if$ one-pass title→palette, first $endif$ closes, no nesting, verbatim unknown
• All $if$ resolved before literal substitutions

Verification

• zig build — clean compile
• zig build test — all tests pass (437/437)

Closes #108