LSP Phase 7: CLI + config plumbing through build_channels

[yogthos]

Phase 7 of 9. Stacked on #30 (Phase 6). The plumbing pass that connects everything end-to-end — by the end of this PR the agent actually gets LSP-aware tools attached to it.

Config schema (`src/config/mod.rs`)

```json
{
"lsp": true // built-ins on
"lsp": false // off entirely
"lsp": { // built-ins on, with per-server overrides
"rust": { "command": ["my-rust-analyzer", "--my-arg"], "env": {"RUST_LOG": "info"} },
"typescript": { "disabled": true }
}
}
```

`LspServerConfig`: `command`, `extensions`, `env`, `initialization`, `disabled` — all optional, missing fields fall back to the built-in defaults.

4 config-parse tests: bool form, per-server map form, absent-is-None (default-on), mixed command/disabled entries.

CLI (`src/cli.rs`)

• `--no-lsp` flag: disables LSP entirely.
• `resolve_lsp_enabled(cli, cfg)` resolver: `no-tools` or `no-lsp` turns it off; otherwise config (default `true`) decides.

Default server commands (`src/lsp/spawn.rs::default_commands`)

Server id	Program	Args
rust	rust-analyzer	—
typescript	typescript-language-server	--stdio
pyright	pyright-langserver	--stdio
clojure-lsp	clojure-lsp	—

Plumbing

`main::build_channels` grows a 10th return slot: `Option<Arc>`. `compile_lsp_commands` merges defaults + user overrides into the spawner command map.

Threaded through:

• `provider::build_agent` + `builder::build_agent_inner` — both get a new `lsp_manager` arg.
• `builder.rs` passes the manager to `WriteTool` / `EditTool` / `ReadTool` (Phase 6 prepared these fields) AND registers `LspTool` when the manager is present (Phase 5's tool now actually attaches).
• `run_interactive` accepts and forwards the manager.
• Plan-switch rebuild passes the live `lsp_manager.clone()` so the rebuilt agent still has LSP tools — same pattern as the bg-store fix.
• 7 slash.rs sub-rebuilds + 2 ui/mod.rs prompt-switch sites pass `None` (intentional — `/model`, `/context-reset` etc. don't need LSP).
• ACP path passes `None` (acp doesn't need LSP for v1).

What this PR doesn't do

• Feature gate: Phase 8 adds `feature = "lsp"` to make the entire module opt-out at compile time. Until then it's always compiled in.
• Docs + manual rust-analyzer test plan: Phase 9.

Test plan

• `cargo build` clean
• `cargo test --bin dirge -- --skip plugin` → 426 passing (was 422; +4 config tests from Phase 7)
• `cargo fmt --check` clean

Next: Phase 8 (feature flag) and Phase 9 (docs + manual end-to-end against real rust-analyzer).