fix(lsp): preserve client and operation state

[mehalter]

Client lifecycle

• Prevent repeated attachment callbacks and preserve progress, formatting, command, and autocommand state.
• Refresh dynamic capabilities and signature triggers as clients register and unregister features.

Operations and compatibility

• Preserve file and folder operation filters, and enforce semantic-token policy across Neovim 0.11 and 0.12.
• Correct related docs and mapping/merge annotations.

Validation

• Passed StyLua, Selene, typos, diff checks, focused runtime tests, and a full tracked-source LuaLS audit.