/feedback opens the Kigi GitHub issues page

Feedback about an unofficial community build belongs on its own issue
tracker, not Moonshot's feedback endpoint — and this mirrors the
official kimi-cli, whose /feedback opens its repo's issues page
(ISSUE_URL in ui/shell/slash.py). /feedback now returns
Action::OpenUrl(https://github.com/ZacharyZhang-NY/Kigi-CLI/issues),
the same battle-tested browser path /docs web uses.

The now-dead TUI text-feedback pipeline is excised: PromptInputMode::
Feedback (~ prefix composer mode), Action::{EnterFeedbackMode,
SendFeedback}, Effect::SendFeedback (the kigi/feedback ACP POST),
TaskResult::{FeedbackComplete,FeedbackFailed}, and their dispatchers.
The shell-side kigi/feedback ACP extension stays: it is protocol
surface for editor embeddings, OAuth-gated, and shared with kigi/btw.

Gates: workspace check/clippy --all-targets 0/0, fmt, kigi-tui lib
6621 passed / 0 failed.

crates/codegen/kigi-tui/src/app/actions.rs

@@ -623,10 +623,6 @@ pub enum Action {
     /// to config.toml). `/plan <desc>` uses `EnterPlanMode` instead
     /// because it also starts a turn.
     SetPlanMode(PlanModeKind),
-    /// Enter feedback mode (visual prompt change, not a send).
-    EnterFeedbackMode,
-    /// Send feedback text collected in feedback mode.
-    SendFeedback(String),
     /// Enter remember mode (visual prompt change, not a send).
     EnterRememberMode,
     /// Send a remember note from # mode. Routes through LLM rewrite when a
@@ -1717,12 +1713,6 @@ pub enum Effect {
     FetchBundleStatus,
     /// Fetch a bundled entry's raw content via `kigi/bundle/entry/get`.
     FetchCatalogEntry { kind: String, name: String },
-    /// Send feedback about the current session (fire-and-forget POST).
-    SendFeedback {
-        agent_id: AgentId,
-        session_id: acp::SessionId,
-        feedback_text: String,
-    },
     /// Save a remember note to global MEMORY.md (async file write).
     SaveMemoryNote {
         agent_id: AgentId,
@@ -2267,15 +2257,6 @@ pub enum TaskResult {
         agent_id: AgentId,
         error: String,
     },
-    /// Feedback submitted successfully (fire-and-forget).
-    FeedbackComplete {
-        agent_id: AgentId,
-    },
-    /// Feedback submission failed.
-    FeedbackFailed {
-        agent_id: AgentId,
-        error: String,
-    },
     /// Memory note saved to global MEMORY.md.
     MemoryNoteSaved {
         agent_id: AgentId,