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

Cargo.toml

@@ -11,6 +11,7 @@ repository = "https://github.com/konstantinfickel/streamd"
 clap = { version = "4", features = ["derive", "env"] }
 clap_complete = "4"
 serde = { version = "1", features = ["derive"] }
+serde_json = "1"
 toml = "1.0"
 thiserror = "2"
 miette = { version = "7", features = ["fancy"] }
@@ -23,6 +24,9 @@ walkdir = "2"
 indexmap = { version = "2", features = ["serde"] }
 itertools = "0.14"
 directories = "6"
+tower-lsp = "0.20"
+tokio = { version = "1", features = ["rt-multi-thread", "io-std"] }
+dashmap = "6"
 
 [dev-dependencies]
 pretty_assertions = "=1.4.1"