refactor: rename scl_lsp → tia_lsp (project umbrella for future STL/LAD/FBD)

Rename the project from scl_lsp to tia_lsp to future-proof for additional
TIA Portal languages (STL/AWL, LAD, FBD). The 'scl' language name is kept
as-is for the SCL filetype and tree-sitter parser; future languages get
their own names (stl, lad, fbd).

Project-wide changes:
- lua/scl_lsp/ → lua/tia_lsp/  (plugin entry point)
- lua/scl/     → lua/tia/      (language modules, shared across TIA langs)
- require('scl.*')    → require('tia.*')
- require('scl_lsp')  → require('tia_lsp')
- LSP client name:    'scl_lsp' → 'tia_lsp'
- Diagnostic source:  'scl_lsp' → 'tia_lsp'  (src/diagnostics.lua)
- package.json name:  'scl-language-server' → 'tia-lsp'

lua/tia_lsp/init.lua:
- Add vim.fn.exepath('tia-lsp') detection so the plugin prefers the
  mason-installed executable and falls back to { 'lua', server_path }
  for manual installs.
- Add opts.ts_parser_url to configure the tree-sitter parser source.
- Remove hardcoded ~/dev/scl_lsp paths in favor of ~/dev/tia-lsp and
  the new ts_parser_url option.

Cleanup:
- Delete lua/tia/init.lua (dead code, unreferenced duplicate of tia_lsp).
- Delete scl_lsp.sh (replaced by the mason-installed bin/tia-lsp wrapper).
- Update README.md and AGENTS.md to reflect the two-repo split
  (tia-lsp server + tia-lsp.nvim plugin) and document Mason installation.

Unchanged (intentional):
- grammar.js, src/grammar.json, src/parser.c: tree-sitter language name
  remains 'scl' (it's the language, not the project).
- Filetype patterns ('scl', 'udt', 'db') in autocmds.
- :SCL* command names (per-filetype prefix; future :STL* etc.).

Tests pass with the same pre-existing failures as before the rename
(formatter VAR_INPUT test, udt_parser line 199 const-variable bug,
plc_json reference-project-missing). No new failures introduced.

AGENTS.md

@@ -1,6 +1,9 @@
-# AGENTS.md - SCL Language Server
+# AGENTS.md - tia-lsp
 
-A Neovim/LazyVim plugin for Siemens SCL language support providing LSP, linting, formatting, syntax highlighting, and auto-completion.
+A Neovim/LazyVim plugin and standalone LSP server for Siemens TIA Portal languages. Currently supports **SCL**; planned support for STL/AWL, LAD, FBD. The project is split into two repos:
+
+- **`tia-lsp`** (this repo) — LSP server (`src/`) + tree-sitter grammar (`grammar.js`). Editor-agnostic.
+- **`tia-lsp.nvim`** — Neovim plugin (`lua/`) that launches the server and adds editor features.
 
 ## Build/Lint/Test Commands
 
@@ -17,7 +20,7 @@ tree-sitter parse <file.scl>  # Parse single SCL file
 
 # Lua Linting
 luacheck src/                 # Lint LSP server code
-luacheck lua/scl/             # Lint plugin modules
+luacheck lua/tia/             # Lint plugin modules
 
 # Unit & Integration Tests
 lua test/run_tests.lua       # Run all tests
@@ -36,18 +39,17 @@ lua test/test_integration.lua # Run integration tests
 ## Project Structure
 
 ```
-scl_lsp/
+tia-lsp/
 ├── src/                     # LSP server (uses dofile)
 │   ├── main.lua            # Entry point, JSON-RPC protocol
-│   ├── parser.lua          # SCL parser
-│   ├── diagnostics.lua     # Linter
+│   ├── parser.lua          # SCL parser (will become parser_scl.lua + dispatch)
+│   ├── diagnostics.lua     # Linter (source = "tia_lsp")
 │   ├── formatter.lua       # Document formatter
 │   ├── treesitter.lua      # Tree-sitter integration
-│   ├── plc_json.lua        # External UDT/DB loading
+│   ├── plc_json.lua        # External UDT/DB loading (language-agnostic)
 │   ├── builtin_instructions.lua  # TIA Portal built-in types
 │   └── json.lua            # JSON encoder/decoder
-├── lua/scl/                 # Neovim plugin (uses require)
-│   ├── init.lua            # Main plugin setup
+├── lua/tia/                 # Neovim plugin (uses require)
 │   ├── udt_parser.lua      # UDT parser
 │   ├── db_parser.lua       # Global DB parser
 │   ├── fb_parser.lua       # Function Block parser
@@ -56,13 +58,24 @@ scl_lsp/
 │   ├── multiline_params.lua
 │   ├── auto_prefix.lua
 │   └── attr_toggle.lua
-├── queries/                 # Tree-sitter queries
-└── grammar.js               # Tree-sitter grammar
+├── lua/tia_lsp/             # Plugin entry point
+│   ├── init.lua            # Main plugin setup (vim.lsp.start)
+│   └── plugins/scl.lua     # LazyVim plugin spec
+├── queries/                 # Tree-sitter queries (per-language: queries/scl/)
+└── grammar.js               # Tree-sitter grammar (language name: 'scl')
 ```
 
+## Naming Convention
+
+- **Project name** (repo, Lua module, LSP server, mason package): `tia-lsp` / `tia_lsp` — umbrella for all TIA languages.
+- **Language name** (filetype, tree-sitter parser, grammar): `scl` — stays as-is. Future languages (`stl`, `lad`, `fbd`) get their own names.
+- **LSP client name**: `tia_lsp` (one client handles all TIA languages; dispatches by `filetype` / `languageId`).
+- **Diagnostic source**: `tia_lsp`.
+- **Commands**: `:SCLFormat`, `:SCLShowVariables`, etc. — per-filetype prefix. Future: `:STLFormat`, etc.
+
 ## Filetype Detection
 
-Required in Neovim config (ftdetect/scl.vim):
+After the split, `ftdetect/scl.vim` will live in `tia-lsp.nvim`. Currently required in Neovim config:
 ```vim
 au BufRead,BufNewFile *.scl set filetype=scl
 au BufRead,BufNewFile *.udt set filetype=scl
@@ -93,12 +106,13 @@ return M
 - Booleans: prefix with `is_`, `has_` (e.g., `is_udt`, `has_members`)
 
 ### Imports
-- `lua/scl/` modules: `require("scl.module_name")`
+- `lua/tia/` modules: `require("tia.module_name")`
+- `lua/tia_lsp/` entry: `require("tia_lsp")`
 - `src/` modules: `dofile(script_path .. "/module.lua")`
 - External dependencies: wrap in `pcall()` for safety
 
 ### Code Formatting
-- `lua/scl/`: 2 spaces indentation
+- `lua/tia/` and `lua/tia_lsp/`: 2 spaces indentation
 - `src/`: tab-based indentation
 - Max line length: 120 characters
 - No trailing whitespace