Make the HIPs the authoritative source of Helm's design philosophy, and sync a copy to helm/helm

## Summary
Establish the HIPs as the authoritative record of Helm's design philosophy, and keep helm/helm's agent-facing copy generated from them. The helm/helm consumption side is helm/helm#32559.

## Stage 2: distribute the philosophy into the HIPs
Working from a sourced philosophy distillation (developer calls, maintainer PR comments, blogs, talks):
- [ ] Audit it against the existing HIPs.
- [ ] Drop anything a HIP already states; reference the HIP instead.
- [ ] Fold the rest into the relevant HIPs, or a new Informational HIP (precedent: HIP-0011, HIP-0017), so the HIPs are complete and authoritative.

## Stage 3: sync bot
- [ ] Build a job that reads all HIPs, distills them, and opens PRs regenerating helm/helm's `AGENTS.md` philosophy section whenever a HIP change merges.

## Notes
- helm/helm cannot link to this repo at review time (Copilot code review reads only in-repo instruction files), so the sync produces an in-repo copy rather than a link.
- Stage 1, the initial hand-built `AGENTS.md` philosophy section, ships first in helm/helm#32559.

Start by auditing the existing HIPs against the sourced philosophy distillation, using HIP-0011 and HIP-0017 as precedents for an Informational HIP. Then define the job that reads the HIPs and regenerates the philosophy section of AGENTS.md for helm/helm, opening a PR after HIP changes merge; completion means the HIPs are authoritative and the copy stays synchronized.

Written by the indexing model from the issue text.