chore(release): expand CHANGELOG for v2.1.17

[glifocat]

Type of Change

• Feature skill - adds a channel or integration (source code changes + SKILL.md)
• Utility skill - adds a standalone tool (code files in .claude/skills/<name>/, no source changes)
• Operational/container skill - adds a workflow or agent skill (SKILL.md only, no source changes)
• Fix - bug fix or security fix to source code
• Simplification - reduces or simplifies source code
• Documentation - docs, README, or CONTRIBUTING changes only

Description

Release-prep bookkeeping: mirror the v2.1.17 release body into CHANGELOG.md so the in-tree changelog matches what's published on GitHub Releases.

Both release tags are already live; this PR is the in-tree mirror only.

• v2.1.0 tag: https://github.com/nanocoai/nanoclaw/releases/tag/v2.1.0
• v2.1.17 tag: https://github.com/nanocoai/nanoclaw/releases/tag/v2.1.17

Scope

• Pure docs — no source, container, or skill changes. Single file touched: CHANGELOG.md.
• Replaces the existing ## [Unreleased] block (which preheld a partial subset of these notes) with a leading empty ## [Unreleased] heading plus the full ## [2.1.17] - 2026-06-17 block, verbatim from the GitHub Release body. Everything from ## [2.1.0] onward is byte-identical to main.
• All cross-doc links are relative docs/... paths, matching the rest of CHANGELOG.md — no absolute github.com URLs in the mirrored block.

Post-merge expectation

bump-version.yml will auto-bump to v2.1.18 after this merges. That's expected post-release housekeeping — the next functional bump rides on top of the mirrored changelog, not on top of the now-empty ## [Unreleased] block.

[mksocial19-code]

Maintainer pass: mostly ready mechanically, with one scope note.\n\nProof:\n- GitHub patch touches only CHANGELOG.md (31 additions / 9 deletions).\n- Local merge onto current origin/main: clean.\n- git diff --check: clean.\n- Compared against the published v2.1.17 release body. The PR mirrors the ## Changes bullet list with repo-relative doc links, but it does not include the release body's intro line, New Contributors, Contributors, or Full Changelog sections.\n\nIf the intended scope is “CHANGELOG gets the release changes,” this is fine. If the intended scope is the PR description's “full release body, verbatim,” it needs either those sections added or the description narrowed. No replacement PR opened because this is a scope/wording choice, not a code fix.