Replace TUI publication commands with agent tools

[nishu-builder]

Remove /pr, /publish-branch and their preview UI in favor of the agent publication and GitHub tools. Remove the orphaned host publication/PR engine, preview plumbing and obsolete publisher tests.

Keep local /import and existing publication records readable. A regression test constructs a legacy publication record and reads its summary and diagnostic after removing the publisher. Update the TUI documentation and specification.

Validation on EC2: Nix build passed. The salted suite passed 46/47 checks in 395s; its Clippy findings were fixed, and Clippy passed on all affected crates with --all-targets -- -D warnings. Formatting passed after those lint-only fixes. HTTPS import/push, shallow-locator/offline-cache, and focused unit checks also passed. The functional suite was not repeated for the lint-only changes.

[nishu-builder]

Layer 8/8. The TUI removal is clean: publication.rs under bin/tui is gone, the Publish/PublishBranch actions, publish_plan, publishing state, the three UiMessage variants and the footer/help text all go together, and the docs (README, SPEC, agent-harness, chat) are updated in the same commit.

One thing the PR title promises and the diff does not do: the host-side publication engine in caos-cli is not removed, only orphaned. At the top of this stack the following are reachable from nothing but their own tests:

• rust/crates/caos-cli/src/publication.rs (the lib one, publish_target with find_or_open_source_tree_pr_in, which shells out to the host's gh)
• source_trees::prepare_publication, resolve_publication_target, publish_target, publish_branch_target, import_publication_base
• publish_source_tree_branch, publish_prepared_source_tree_branch, push_publication, append_publication_pending/terminal, same_publication_intent, origin_repository in lib.rs
• host_git::find_or_open_source_tree_pr_in, validate_pr_source_tree, pr_base_is_ancestor

That is several hundred lines of a second publication implementation (implementation: "caos-cli/preserve" alongside the new "caos/server-push") with its own lease, recovery and PR-creation logic, plus the git-locator dependency #250 added to caos-cli only to share two helpers with it. None of it warns because it is pub. If the intent is to keep a host fallback, the design doc should say so and something should call it; otherwise this PR is the natural place to delete it, since it is the one that removes the only caller. The publication-record reading paths (publications(), publication_diagnostic) are separate and should stay, as agent-publish.md says existing records remain readable.

Also: this PR's base is #254, and the stack description on #248 lists it last, but its number is the lowest. Just noting for whoever merges bottom-up that the order is by base branch, not by PR number.

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Generated by Claude Code

[nishu-builder]

Closing with the rest of stack #261. Removing /pr and /publish-branch is being redone as the top of a new stack: #300 (design), then the github tool, then the removal.

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Generated by Claude Code