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

* Link issues and meeting notes in Open Questions README row

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* 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/skill-uri-scheme.md

@@ -3,7 +3,7 @@
 > Proposed convention for identifying skill resources over MCP.
 
 **Issue:** [#44](https://github.com/modelcontextprotocol/experimental-ext-skills/issues/44)
-**Status:** Incorporated into the draft [Skills Extension SEP](https://github.com/modelcontextprotocol/experimental-ext-skills/pull/69). This survey informed the SEP's URI scheme design; see also [PR #70](https://github.com/modelcontextprotocol/experimental-ext-skills/pull/70) for subsequent refinements (multi-segment paths, path-name decoupling).
+**Status:** Incorporated into the draft [Skills Extension SEP](https://github.com/modelcontextprotocol/experimental-ext-skills/pull/69), now submitted to the MCP spec as [SEP-2640](https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2640). This survey informed the SEP's URI scheme design; see also [PR #70](https://github.com/modelcontextprotocol/experimental-ext-skills/pull/70) for subsequent refinements (multi-segment paths, path-name decoupling).
 
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