feat(tauri-app): expand tray menu + open_external_url + Profile/Search items

Tray menu now has:
  Show maarcadetweet
  Home
  Compose
  Profile
  Search
  ----
  Quit

The Home/Profile/Search items emit 'app://navigate' events
which the frontend's listenTrayEvents translates to view
switches. The compose and show events continue to be
separate event types ('app://compose', 'app://show').

open_external_url Tauri command takes a URL, validates it's
http(s), and uses tauri-plugin-shell to open it in the user's
default browser. The frontend's openExternalUrl falls back
to window.open in the browser preview (no Tauri runtime).

svelte-check error fix: tauriCall<T>(cmd, fallback, args?)
had the second call argument as 'undefined' instead of 'null'
on the call site for session.load(). The TypeScript compiler
correctly noted that the fallback type 'T' (here Session |
null) couldn't be undefined. Replaced with 'null' and
dropped the trailing null args argument (it's optional).

crates/tauri-app/src-tauri/Cargo.lock

@@ -2435,6 +2435,25 @@ version = "2.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d98f6fed1fde3f8c21bc40a1abb88dd75e67924f9cffc3ef95607bad8017f8e2"
 
+[[package]]
+name = "is-docker"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "928bae27f42bc99b60d9ac7334e3a21d10ad8f1835a4e12ec3ec0464765ed1b3"
+dependencies = [
+ "once_cell",
+]
+
+[[package]]
+name = "is-wsl"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "173609498df190136aa7dea1a91db051746d339e18476eed5ca40521f02d7aa5"
+dependencies = [
+ "is-docker",
+ "once_cell",
+]
+
 [[package]]
 name = "iterator-sorted"
 version = "0.1.0"
@@ -2735,6 +2754,7 @@ dependencies = [
  "tauri-plugin-dialog",
  "tauri-plugin-keyring-store",
  "tauri-plugin-notification",
+ "tauri-plugin-shell",
  "tauri-plugin-updater",
  "tauri-plugin-window-state",
  "tokio",
@@ -3286,6 +3306,17 @@ version = "0.3.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "c08d65885ee38876c4f86fa503fb49d7b507c2b62552df7c70b2fce627e06381"
 
+[[package]]
+name = "open"
+version = "5.3.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cd8d3b65c44123a56e0133d2cd06ce4361bd3ca99d41198b2f25e3c3db9b8b4a"
+dependencies = [
+ "dunce",
+ "is-wsl",
+ "libc",
+]
+
 [[package]]
 name = "openssl"
 version = "0.10.81"
@@ -3345,6 +3376,16 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "os_pipe"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7d8fae84b431384b68627d0f9b3b1245fcf9f46f6c0e3dc902e9dce64edd1967"
+dependencies = [
+ "libc",
+ "windows-sys 0.61.2",
+]
+
 [[package]]
 name = "osakit"
 version = "0.3.1"
@@ -4526,12 +4567,44 @@ dependencies = [
  "lazy_static",
 ]
 
+[[package]]
+name = "shared_child"
+version = "1.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e362d9935bc50f019969e2f9ecd66786612daae13e8f277be7bfb66e8bed3f7"
+dependencies = [
+ "libc",
+ "sigchld",
+ "windows-sys 0.60.2",
+]
+
 [[package]]
 name = "shlex"
 version = "2.0.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f8fadd59c855ef2080decdef8ff161eb6661b86933c9d82e5ba29dc602a55aba"
 
+[[package]]
+name = "sigchld"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "47106eded3c154e70176fc83df9737335c94ce22f821c32d17ed1db1f83badb1"
+dependencies = [
+ "libc",
+ "os_pipe",
+ "signal-hook",
+]
+
+[[package]]
+name = "signal-hook"
+version = "0.3.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d881a16cf4426aa584979d30bd82cb33429027e42122b169753d6ef1085ed6e2"
+dependencies = [
+ "libc",
+ "signal-hook-registry",
+]
+
 [[package]]
 name = "signal-hook-registry"
 version = "1.4.8"
@@ -5087,6 +5160,27 @@ dependencies = [
  "url",
 ]
 
+[[package]]
+name = "tauri-plugin-shell"
+version = "2.3.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8457dbf9e2bab1edd8df22bb2c20857a59a9868e79cb3eac5ed639eec4d0c73b"
+dependencies = [
+ "encoding_rs",
+ "log",
+ "open",
+ "os_pipe",
+ "regex",
+ "schemars 0.8.22",
+ "serde",
+ "serde_json",
+ "shared_child",
+ "tauri",
+ "tauri-plugin",
+ "thiserror 2.0.18",
+ "tokio",
+]
+
 [[package]]
 name = "tauri-plugin-updater"
 version = "2.10.1"