docs: link SEP-2640 across repo and tidy Related Work table (#90)

* Update documentation for Skills Extension SEP and related resources

- Revised links and descriptions in README.md to reflect the submitted Skills Extension SEP (PR #2640).
- Updated current status in approaches.md to indicate submission of the Skills Extension SEP.
- Clarified tracking information in open-questions.md regarding the Skills Extension SEP submission.
- Adjusted related work in related-work.md to include the Skills Extension SEP and mark a rejected proposal.
- Changed status in sep-draft-skills-extension.md to 'submitted' and updated author information.
- Enhanced skill-uri-scheme.md to indicate the incorporation of feedback into the submitted Skills Extension SEP.

* Move rejected SEP-2093 to the bottom of SEPs and Proposals table

Keeps the list active-proposals-first so readers aren't distracted by the
struck-out entry.

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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Mark SEP-2076 as closed and move to the bottom of proposals table

PR #2076 was closed without merge on 2026-02-24.

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* Use SEP-2640 naming convention per MCP SEP guidelines

Per https://modelcontextprotocol.io/community/sep-guidelines, a submitted
SEP is named "SEP-<PR-number>". Rename in-repo references from "PR #2640"
to "SEP-2640" and update the draft doc heading from the "SEP-0000"
placeholder to "SEP-2640".

Also mark Approach 1's SEP-2076 status as closed (2026-02-24, no sponsor
found); approaches.md still listed it as "Draft, seeking sponsor".

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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Fix SEP-2076 closure rationale

Closure followed the WG's decision to first explore a convention-based
approach using existing primitives, not a sponsor issue.

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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Refine SEP-2640 description in README to clarify proposal details

* Link issues and meeting notes in Open Questions README row

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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Surface SEP-2640 in README and related-work table order

README: move the Skills Extension SEP from the bottom of the Repository
Contents table to sit after Approaches, matching the narrative flow
(framing → options → proposal → supporting material).

related-work.md: lead the SEPs and Proposals table with SEP-2640 (this
WG's headline proposal), followed by the prerequisite PR #2527.

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Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Add 'Open work' link to README header pointing to open PRs

Signals that alternative proposals, decisions, implementations, and
other in-flight contributions are welcome — SEP-2640 is one direction,
not the only one.

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---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

docs/related-work.md

@@ -4,10 +4,11 @@
 
 | Proposal | Venue | Description |
 | :--- | :--- | :--- |
-| [SEP-2076](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2076) | MCP Spec | Agent Skills as a first-class MCP primitive |
-| [SEP-2093](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2093) | MCP Spec | Resource Contents Metadata and Capabilities: scoped `resources/list`, per-resource capabilities, `resources/metadata` endpoint |
+| [SEP-2640 (Skills Extension)](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640) | MCP Spec | This WG's proposed extension: skills served over MCP using the Resources primitive and `skill://` URI scheme ([working draft](sep-draft-skills-extension.md)) |
 | [PR #2527](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2527) | MCP Spec | Recommend clients expose resource read to models — prerequisite for the resources-based skills approach |
 | [skills.json format proposal](https://github.com/modelcontextprotocol/registry/discussions/895) | MCP Registry | Skills metadata in registry schema |
+| ~~[SEP-2093](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2093)~~ | MCP Spec | ~~Resource Contents Metadata and Capabilities: scoped `resources/list`, per-resource capabilities, `resources/metadata` endpoint~~ — **rejected** ([labeled upstream](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2093)) |
+| ~~[SEP-2076](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2076)~~ | MCP Spec | ~~Agent Skills as a first-class MCP primitive~~ — **closed** (2026-02-24, without merge) |
 
 ## Working Group Member Implementations