fix: stop amputating RC suffixes from docs URLs (#23903)

Fixes #23897 (docs link only — naming rename is in #23905)

- Fix version stripping logic in both Go (`codersdk/deployment.go`) and
TypeScript (`site/src/utils/docs.ts`) to preserve `-rc.X` suffixes
instead of amputating them along with `-devel`
- Add `v0.0.0` fallback in the TS frontend to match Go backend behavior
for dev builds
- Add tests covering RC, devel, and plain release version strings

> 🤖 Written by a Coder Agent. Will be reviewed by a human.

codersdk/deployment.go

@@ -1251,7 +1251,11 @@ func DefaultSupportLinks(docsURL string) []LinkConfig {
 }
 
 func removeTrailingVersionInfo(v string) string {
-	return strings.Split(strings.Split(v, "-")[0], "+")[0]
+	// Strip build metadata (everything after '+').
+	v, _, _ = strings.Cut(v, "+")
+	// Strip '-devel' suffix if present.
+	v = strings.TrimSuffix(v, "-devel")
+	return v
 }
 
 func DefaultDocsURL() string {

codersdk/deployment_internal_test.go

@@ -25,10 +25,36 @@ func TestRemoveTrailingVersionInfo(t *testing.T) {
 			Version:                    "v2.16.0+683a720-devel",
 			ExpectedAfterStrippingInfo: "v2.16.0",
 		},
+		// RC versions: preserve the -rc.X suffix, strip build metadata.
+		{
+			Version:                    "v2.32.0-rc.1+abc123",
+			ExpectedAfterStrippingInfo: "v2.32.0-rc.1",
+		},
+		{
+			Version:                    "v2.32.0-rc.0",
+			ExpectedAfterStrippingInfo: "v2.32.0-rc.0",
+		},
+		{
+			Version:                    "v2.32.0-rc.1+683a720-devel",
+			ExpectedAfterStrippingInfo: "v2.32.0-rc.1",
+		},
+		// Bare devel suffix, no build metadata.
+		{
+			Version:                    "v2.32.0-devel",
+			ExpectedAfterStrippingInfo: "v2.32.0",
+		},
+		// Plain release, identity case.
+		{
+			Version:                    "v2.16.0",
+			ExpectedAfterStrippingInfo: "v2.16.0",
+		},
 	}
 
 	for _, tc := range testCases {
-		stripped := removeTrailingVersionInfo(tc.Version)
-		require.Equal(t, tc.ExpectedAfterStrippingInfo, stripped)
+		t.Run(tc.Version, func(t *testing.T) {
+			t.Parallel()
+			stripped := removeTrailingVersionInfo(tc.Version)
+			require.Equal(t, tc.ExpectedAfterStrippingInfo, stripped)
+		})
 	}
 }