fix(summarise): use template.lock/RhizaTemplate model for template info; add output customisation flags

[Copilot]

rhiza summarise hardcoded jebel-quant/rhiza as the template reference whenever template.yml was absent or used the newer repository:/ref: key format. The last-sync grep also hardcoded "rhiza" in commit patterns, missing non-rhiza templates entirely.

Bug fixes

• get_template_info() — replaced ad-hoc line-by-line YAML parsing with TemplateLock.from_yaml() (preferred, authoritative) → RhizaTemplate.from_yaml() fallback. Handles both template-repository/repository and template-branch/ref key formats. Returns ("", "") instead of hardcoding "jebel-quant/rhiza" when no config exists.
• get_last_sync_date() — reads synced_at from template.lock first; builds git-log grep patterns from the actual template short name instead of the literal string "rhiza".

New output customisation options

CLI flag	Effect
--no-header / --no-footer	Suppress header or footer blocks
--no-categories	Flat file list instead of grouped categories
--format markdown|plain|json	Switch output format
--title <str>	Override the section heading
--compare <ref>	Diff working tree against a git ref instead of staged index
--template <file.j2>	Render output via a custom Jinja2 template

The Jinja2 template context exposes: template_repo, template_branch, last_sync, sync_date, changes (added/modified/deleted lists), categories (dict), title.

Categorisation improvements

src/ → Source Code, docs/ → Documentation (alongside existing book/).