fix(peer): apply catalog portability rules in validate_relative_path

Security audit finding EXP2-SEC-03. `path_validation.rs` guarded
against traversal, UNC prefixes, drive letters and symlink escapes, but
unlike the catalog validators in lanspread-db it did not reject Windows
device names (CON, NUL, COM1..9, LPT1..9), components with a trailing
dot or space, reserved characters (`<>:"|?*`), or control characters.
On Windows, opening `NUL.txt` talks to a device and `file.txt.` is
silently rewritten to `file.txt`, so such names must never reach the
filesystem.

The catalog component validator is now exported from lanspread-db as
`validate_portable_component` and applied to every normal component in
`validate_relative_path`. The only current caller is Stream Install's
staging-path resolution, whose inputs are already canonical catalog
paths, so this changes nothing for valid archives; it removes a
divergence between two validators that are supposed to agree.

Test plan: `just test` (new cases cover device names in any position,
trailing dot/space, a reserved character and a control character, and
confirm `console.txt` and `com10.txt` stay valid).

Claude-Session: https://claude.ai/code/session_017C3Nbgwpdm3YNwZhhFLHwg

crates/lanspread-db/src/content_manifest/mod.rs

@@ -41,7 +41,7 @@ pub use model::{
     MAX_CATALOG_PATH_BYTES,
     MAX_CATALOG_TOTAL_BYTES,
 };
-pub use path::CanonicalCatalogPath;
+pub use path::{CanonicalCatalogPath, validate_portable_component};
 pub use store::{
     CATALOG_PUBLICATION_MARKER_NAME,
     CatalogManifestStore,

crates/lanspread-db/src/content_manifest/path.rs

@@ -164,6 +164,17 @@ fn validate_path(path: &str) -> eyre::Result<()> {
     Ok(())
 }
 
+/// Validates one path component under the portable catalog rules: no
+/// `.`/`..`, at most 255 bytes, no trailing dot or space, no control or
+/// Windows-reserved characters, and no Windows device name stem.
+///
+/// # Errors
+///
+/// Returns the first violated rule.
+pub fn validate_portable_component(component: &str) -> eyre::Result<()> {
+    validate_component(component)
+}
+
 fn validate_component(component: &str) -> eyre::Result<()> {
     if component.is_empty() || matches!(component, "." | "..") {
         eyre::bail!("catalog path contains a non-canonical component: {component:?}");