Execute the DP→GP rename as the first live migration

The execution half of #29, running on the machinery from #54. Blocked on #54 rung 2.

The rename itself, decided in #29: **design principles → guiding principles**, `DP-00N` → `GP-00N`. Three-letter-adjacent prefix retained on purpose; "DP" was always a slightly cursed abbreviation. The companion "architecture → atomic decision records" relabel is rung 0 — prose only, no codes move — and rides along as the worked example of the cheapest rung.

Spec: `record/migrations.d/0001-dp-to-gp.toml` (scaffolded by `luria new migration`), a single `rename_scheme` operation. What the run must produce:

- `[luria.schemes.DP]` → `[luria.schemes.GP]` in `luria.toml` and `template/luria.toml`; output becomes `docs/guiding-principles.md`; the `[luria.paths]` key follows.
- `git mv record/principles.d/DP-00N.md → GP-00N.md` (9 documents), each stamped `formerly: [DP-N]`.
- Mapping-driven sweep of every reference: link targets, labels, and anchors (`#dp-N` → `#gp-N`), historical journal and changelog files included — full rewrite per the ADR-040 doctrine, one spelling tree-wide.
- **Not touched:** fixture `DP-018` in `tests/test_remotes.py`, example `DP-004` in `remotes.py` (both carry `unresolved-ok` excuses), and `SG-DP-18` / `[luria.remotes.SG.schemes.DP]` — strata-g's namespace is theirs.
- Migration commit appended to `.git-blame-ignore-revs` by the tooling.
- `luria lint` green with zero `legacy-spellings` warnings in-tree afterwards; branches in flight get modernized by `luria link --fix` on their next touch.

This run is the acceptance test for the machinery: if the DP→GP migration needs hand-editing beyond writing the spec file, rung 2 isn't done.

Start with record/migrations.d/0001-dp-to-gp.toml and the machinery from #54, noting that this issue is blocked on rung 2. Execute the migration and check that the nine documents, configuration paths, references, history files, blame-ignore entry, and lint output match the stated acceptance criteria while the listed fixtures and strata-g namespace remain untouched.

Written by the indexing model from the issue text.