chore(migration): repoint every published link off GitHub

The canonical repo is git.zacharyzhang.com now, so every URL a user can
actually reach had to move with it.

Self-updater: `PRODUCTION_ENDPOINTS.update_base_url` targets Gitea's
`/api/v1/repos/.../releases`, which serves the same wire format GitHub's
releases API did — `Release`/asset deserialisation is unchanged. The alpha
channel requests `?per_page=30&limit=30` because GitHub reads the page size
from `per_page` and Gitea from `limit`, and each ignores the other's, so one
URL stays correct on either.

Installers: same API base, and the documented one-liners become
`https://kigicli.dev/install.{sh,ps1}`. That domain's Worker proxies both
files from Gitea raw `main`, so the published install command survives any
future forge move without being reprinted everywhere. install.ps1 also drops
the GitHub-specific `Accept: application/vnd.github+json`.

Everything else user-facing: `/feedback` and the shell's feedback fallback
point at the Gitea issue tracker, `/docs` at the Gitea-rendered README, and
web_fetch's User-Agent at kigicli.dev. SECURITY.md now routes reports to the
issue tracker with a warning to withhold exploitable detail, because Gitea
has no equivalent of GitHub's private vulnerability reporting. Comments
naming `.github/workflows/release.yml` name `.gitea/` now.

Tests assert against these constants rather than literal URLs, so they
follow automatically; the one URL-shape assertion (production endpoints are
https) still holds.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/codegen/kigi-shell/src/agent/feedback_client.rs

@@ -3,7 +3,7 @@
 //! Port of kimi-cli's `/feedback` slash command (kimi-cli
 //! `src/kimi_cli/ui/shell/slash.py`, `feedback()`): subscription (OAuth)
 //! sessions POST the user's feedback text to `{coding_api_base_url}/feedback`
-//! with a Bearer token; everyone else is pointed at the GitHub issue tracker.
+//! with a Bearer token; everyone else is pointed at the project issue tracker.
 //! The request body carries exactly the fields kimi-cli sends:
 //! `session_id`, `content`, `version`, `os`, `model`.
 
@@ -12,7 +12,8 @@ use std::sync::Arc;
 use serde::Serialize;
 
 /// Where non-subscription users (no OAuth session) submit feedback instead.
-pub const FEEDBACK_ISSUES_URL: &str = "https://github.com/ZacharyZhang-NY/Kigi-CLI/issues";
+pub const FEEDBACK_ISSUES_URL: &str =
+    "https://git.zacharyzhang.com/ZacharyZhang-NY/Kigi-CLI/issues";
 
 /// HTTP error from the feedback endpoint with a preserved status code, so
 /// callers can distinguish auth failures (401) without string matching.