feat: add streamd lsp subcommand with LSP server

Implements a full Language Server Protocol server accessible via
`streamd lsp`. The server communicates over stdin/stdout and auto-
detects the workspace root from the LSP initialize request.

Features implemented:
- Passive mode when no .streamd.toml exists in workspace root
- Workspace-root-based config loading (bypasses R22/R23 global config)
- .streamd.toml file watcher (config reloads without restart)
- textDocument/completion with @ trigger, conditional suggestions
  (if_with relationships), and temporal date/time snippets (R16)
- textDocument/publishDiagnostics: R15 file-name format + R18
  timesheet violations (overlapping timecards, unclosed days)
- textDocument/documentSymbol: shard tree exposed as nested symbols
- textDocument/codeAction: "Mark task as done" quickfix for @Task
- workspace/symbol: cross-file shard search
- textDocument/references: find all @Marker occurrences
- textDocument/rename: rename @Marker across all files

Dependencies added: tower-lsp 0.20, tokio, dashmap, serde_json

src/cli/args.rs

@@ -72,4 +72,7 @@ pub enum Commands {
         #[arg(value_enum)]
         shell: Shell,
     },
+
+    /// Start LSP server (communicates over stdin/stdout)
+    Lsp,
 }

src/cli/commands/mod.rs

@@ -12,6 +12,7 @@ use crate::models::{LocalizedShard, RepositoryConfiguration};
 pub mod completions;
 pub mod daily;
 pub mod edit;
+pub mod lsp;
 pub mod new;
 pub mod timesheet;
 pub mod todo;

src/main.rs

@@ -22,6 +22,7 @@ fn main() -> miette::Result<()> {
         Some(Commands::Completions { shell }) => {
             streamd::cli::commands::completions::run(shell);
         }
+        Some(Commands::Lsp) => streamd::cli::commands::lsp::run()?,
         None => streamd::cli::commands::daily::run(None)?,
     }