Make agent docs self-contained without external-repo pointers

.github/copilot-instructions.md

@@ -153,4 +153,4 @@ After the final push, sweep-resolve stale older threads for removed code paths.
 
 Read [AGENTS.md](../AGENTS.md) for this repo's conventions and [../ARCHITECTURE.md](../ARCHITECTURE.md) for PlexCleaner's architecture, processing pipeline, and design patterns. For code-style rules, [`CODESTYLE.md`](../CODESTYLE.md) is authoritative. Don't restate any of these files' rules in commit bodies or PR descriptions - keep those focused on the change itself.
 
-**In a derived repo:** if you find a discrepancy that should be fixed in the template itself (this file or AGENTS.md is out of date, a rule is missing, something bit this repo and would bite the next), open an issue upstream in [`ptr727/ProjectTemplate`](https://github.com/ptr727/ProjectTemplate) rather than only fixing it locally - see the template's [AGENTS.md "Staying in Sync and Reporting Drift Upstream"](https://github.com/ptr727/ProjectTemplate/blob/main/AGENTS.md#staying-in-sync-and-reporting-drift-upstream).
+**Shared conventions:** if you find a discrepancy that looks like it should be fixed in the shared conventions rather than only locally (this file or AGENTS.md is out of date, a rule is missing, something bit this repo and would bite the next), raise it with the maintainer rather than only patching it here.

CODESTYLE.md

@@ -35,7 +35,7 @@ These apply repo-wide, in every directory:
 
 1. **Markdown linting**: All `.md` files must be lint-clean (error and warning free) via the VS Code `markdownlint` extension. [`.markdownlint-cli2.jsonc`](./.markdownlint-cli2.jsonc) at the repo root is the single source of truth - the davidanson `markdownlint` extension and a command-line `markdownlint-cli2` run both read it, so the IDE and CLI stay in lock-step. Rules it deliberately disables (e.g. `MD013` line-length, `MD033` inline HTML) are **intentional** - do not "fix" them. Fix violations at the source rather than disabling rules.
 2. **Spelling**: All spelling must be clean via the CSpell VS Code integration; words must be correctly spelled in **US English** (the repo-wide convention - see [AGENTS.md](./AGENTS.md)). Project-specific terms go in the workspace CSpell config.
-3. **Spelling CI scope**: The enforced CI spell-check gate covers **`README.md` and `HISTORY.md` only** - these are the files every repo visitor sees, so they must be clean. It is deliberately **not** all `**/*.md`: repos carry many markdown files full of technical terms, and gating every one of them would mean endlessly padding `cspell.json` just to keep CI green. Broad, live spell-checking across any file (source, markdown, text) is the **cspell editor extension's** job, so typos still surface to whoever is editing. A repo owner **may** widen their own CI file list, but the template ships README + HISTORY as the default; keep every surface that runs cspell - the CI workflow and any local VS Code task or one-liner the repo has - on the same file list. The list is explicit (not a glob), so a repo that ships no `HISTORY.md` (e.g. one with no changelog) must drop it from all three surfaces and gate on `README.md` alone - cspell errors on a listed file that does not exist. Markdown *linting* (item 1) stays repo-wide `**/*.md` - it does not choke on technical terms.
+3. **Spelling CI scope**: The enforced CI spell-check gate covers **`README.md` and `HISTORY.md` only** - these are the files every repo visitor sees, so they must be clean. It is deliberately **not** all `**/*.md`: repos carry many markdown files full of technical terms, and gating every one of them would mean endlessly padding `cspell.json` just to keep CI green. Broad, live spell-checking across any file (source, markdown, text) is the **cspell editor extension's** job, so typos still surface to whoever is editing. A repo owner **may** widen their own CI file list, but README + HISTORY are the default; keep every surface that runs cspell - the CI workflow and any local VS Code task or one-liner the repo has - on the same file list. The list is explicit (not a glob), so a repo that ships no `HISTORY.md` (e.g. one with no changelog) must drop it from all three surfaces and gate on `README.md` alone - cspell errors on a listed file that does not exist. Markdown *linting* (item 1) stays repo-wide `**/*.md` - it does not choke on technical terms.
 
 ## .NET