chore: bump Go toolchain version to 1.26.2 (#24975)

## Summary
Bumps the repository Go toolchain from 1.25.9 to 1.26.2 across local
development, CI, dogfood Docker images, and Nix builds.

## Changes
- Update `go.mod` and the shared setup-go action to Go 1.26.2.
- Update dogfood Ubuntu image Go versions and the official linux-amd64
tarball checksum.
- Move Nix Go module builds from `buildGo125Module` to
`buildGo126Module`.
- Regenerate API docs affected by Go 1.26 stdlib URL documentation
changes.

## Validation
- `./scripts/check_go_versions.sh`
- `make fmt`
- `make lint`
- `make build-slim`
- `make test TEST_SHORT=1`
- `make pre-commit`

> 🤖 This PR was created with the help of Coder Agents, and needs a human
review. 🧑💻

coderd/apidoc/docs.go

@@ -26415,19 +26415,19 @@ const docTemplate = `{
             "type": "object",
             "properties": {
                 "forceQuery": {
-                    "description": "append a query ('?') even if RawQuery is empty",
+                    "description": "ForceQuery indicates whether the original URL contained a query ('?') character.\nWhen set, the String method will include a trailing '?', even when RawQuery is empty.",
                     "type": "boolean"
                 },
                 "fragment": {
-                    "description": "fragment for references, without '#'",
+                    "description": "fragment for references (without '#')",
                     "type": "string"
                 },
                 "host": {
-                    "description": "host or host:port (see Hostname and Port methods)",
+                    "description": "\"host\" or \"host:port\" (see Hostname and Port methods)",
                     "type": "string"
                 },
                 "omitHost": {
-                    "description": "do not emit empty host (authority)",
+                    "description": "OmitHost indicates the URL has an empty host (authority).\nWhen set, the String method will not include the host when it is empty.",
                     "type": "boolean"
                 },
                 "opaque": {
@@ -26439,15 +26439,15 @@ const docTemplate = `{
                     "type": "string"
                 },
                 "rawFragment": {
-                    "description": "encoded fragment hint (see EscapedFragment method)",
+                    "description": "RawFragment is an optional field containing an encoded fragment hint.\nSee the EscapedFragment method for more details.\n\nIn general, code should call EscapedFragment instead of reading RawFragment.",
                     "type": "string"
                 },
                 "rawPath": {
-                    "description": "encoded path hint (see EscapedPath method)",
+                    "description": "RawPath is an optional field containing an encoded path hint.\nSee the EscapedPath method for more details.\n\nIn general, code should call EscapedPath instead of reading RawPath.",
                     "type": "string"
                 },
                 "rawQuery": {
-                    "description": "encoded query values, without '?'",
+                    "description": "RawQuery contains the encoded query values, without the initial '?'.\nUse URL.Query to decode the query.",
                     "type": "string"
                 },
                 "scheme": {

coderd/apidoc/swagger.json

@@ -24386,19 +24386,19 @@
 			"type": "object",
 			"properties": {
 				"forceQuery": {
-					"description": "append a query ('?') even if RawQuery is empty",
+					"description": "ForceQuery indicates whether the original URL contained a query ('?') character.\nWhen set, the String method will include a trailing '?', even when RawQuery is empty.",
 					"type": "boolean"
 				},
 				"fragment": {
-					"description": "fragment for references, without '#'",
+					"description": "fragment for references (without '#')",
 					"type": "string"
 				},
 				"host": {
-					"description": "host or host:port (see Hostname and Port methods)",
+					"description": "\"host\" or \"host:port\" (see Hostname and Port methods)",
 					"type": "string"
 				},
 				"omitHost": {
-					"description": "do not emit empty host (authority)",
+					"description": "OmitHost indicates the URL has an empty host (authority).\nWhen set, the String method will not include the host when it is empty.",
 					"type": "boolean"
 				},
 				"opaque": {
@@ -24410,15 +24410,15 @@
 					"type": "string"
 				},
 				"rawFragment": {
-					"description": "encoded fragment hint (see EscapedFragment method)",
+					"description": "RawFragment is an optional field containing an encoded fragment hint.\nSee the EscapedFragment method for more details.\n\nIn general, code should call EscapedFragment instead of reading RawFragment.",
 					"type": "string"
 				},
 				"rawPath": {
-					"description": "encoded path hint (see EscapedPath method)",
+					"description": "RawPath is an optional field containing an encoded path hint.\nSee the EscapedPath method for more details.\n\nIn general, code should call EscapedPath instead of reading RawPath.",
 					"type": "string"
 				},
 				"rawQuery": {
-					"description": "encoded query values, without '?'",
+					"description": "RawQuery contains the encoded query values, without the initial '?'.\nUse URL.Query to decode the query.",
 					"type": "string"
 				},
 				"scheme": {