Add per-type SYSTEM_CONTEXT starter variants to repo bootstrap

[quackerjeff]

Summary

Add repository-type-specific SYSTEM_CONTEXT starter templates to improve the output of scripts/seed-repo.sh.

Problem

The current bootstrap flow creates one generic SYSTEM_CONTEXT.md file for every repo type. That is a good baseline, but it leaves too much manual editing for common repo profiles such as ui, api, worker, data, fullstack, and platform.

Proposed enhancement

Add starter variants such as:

• templates/repo/system-context-ui.md.tmpl
• templates/repo/system-context-api.md.tmpl
• templates/repo/system-context-worker.md.tmpl
• templates/repo/system-context-data.md.tmpl
• templates/repo/system-context-fullstack.md.tmpl
• templates/repo/system-context-platform.md.tmpl

Then update scripts/seed-repo.sh to:

• select the matching type-specific template when available
• fall back to the generic templates/SYSTEM_CONTEXT.md when no type-specific template exists

Expected benefit

• better repo-specific guidance out of the box
• less placeholder cleanup after seeding
• stronger architectural grounding for AI agents in newly created repos
• better alignment between repo type and local context documents

Acceptance criteria

• type-specific SYSTEM_CONTEXT templates exist for the supported repo profiles
• seed-repo.sh renders the matching variant for each repo type
• generic fallback still works
• BOOTSTRAPPING.md documents the behavior