fix(lsp): encode reserved chars in workspace root URIs

[dergachoff]

Closes #221.

Problem

initialize built workspace folder URIs by splicing raw paths, so a workspace root containing reserved characters was sent wrong or rejected:

• # parsed cleanly but truncated. /home/me/dev/#work became path /home/me/dev/ with fragment work, so the server silently received the parent directory as its root.
• [ and ] were rejected by Uri::from_str, failing initialization with Invalid workspace root.

Root cause

lsp/lifecycle.rs predates bridge::path_to_uri (#151) and never used it, so it carried its own format!("file://{path_str}") plus a duplicate copy of the Windows \\?\ stripping the shared helper already does.

Fix

Route the mapping through the shared encoder. path_to_uri panics and this call site returns Result, so try_path_to_uri becomes the fallible core and path_to_uri a thin wrapper over it; the new helper is crate-internal. The per-root mapping moves into workspace_folder so it is testable without a live LSP client.

Incidental: the Invalid UTF-8 in path branch is gone, since Url::from_file_path takes a &Path. Non-UTF-8 roots now work instead of erroring.

Validation

• cargo +nightly fmt --check, cargo +1.95 clippy --all-targets --all-features -- -D warnings
• cargo +1.95 nextest run — 412 passed, 33 skipped
• cargo +1.95 check -p mcpls-core --target x86_64-pc-windows-msvc --all-targets --all-features, since fix(core): encode reserved path chars in file URIs #151 hit Windows-only breakage. New tests use C:\... roots on Windows and /... elsewhere, matching state.rs.
• The three new workspace_folder tests fail against the pre-fix logic with the predicted symptom: left: "file:///home/me/dev/#work", right: "file:///home/me/dev/%23work".