prompts: remove /home/user path examples that bias tilde expansion

- file_grep.meta: replace /home/user/project with /abs/path
- system_prompt.md: use $XDG_CONFIG_HOME instead of ~
- agent-copilot.md: use relative path in code block example

cmd/olliesrv/internal/prompts/system_prompt.md

@@ -33,7 +33,7 @@ Tools are loaded at startup. Additional tools can be loaded at runtime via the `
 - To search: call `file_grep` directly, NOT `grep` via shell
 - To edit: call `file_edit` directly, NOT `sed` via shell
 
-The tool scripts in `~/.config/ollie/tools/` are already exposed as callable functions. Never invoke them via their filesystem path — call them by name through the tool interface.
+The tool scripts in `$XDG_CONFIG_HOME/ollie/tools/` are already exposed as callable functions. Never invoke them via their filesystem path — call them by name through the tool interface.
 
 Shell is for system commands that have no native tool equivalent: builds, git, package managers, interpreters, etc.
 

data/prompts/agent-copilot.md

@@ -47,7 +47,7 @@ Example response:
 
 > The null check on line 42 is inverted — it should guard against nullptr, not assert it.
 >
-> ```cpp /home/user/src/main.cpp:42-44
+> ```cpp src/main.cpp:42-44
 > if (ptr == nullptr) {
 >     return;
 > }

data/tools/file_grep.meta

@@ -1,6 +1,6 @@
 {
   "description": "Search file contents with ripgrep. Capped at 50 matches by default.",
-  "prompt": "## file_grep\n\nSearch file contents with ripgrep. Capped at 50 matches by default.\n\n**Args**: `pattern` (required), plus optional named params.\n\n```\nfile_grep(pattern=\"pattern\", path=\"/abs/dir\")\nfile_grep(pattern=\"TODO\", path=\"src/\", glob=\"*.go\", case_insensitive=true)\nfile_grep(pattern=\"func main\", path=\"/home/user/project\")\n```\n\n- `path`: search directory (not a positional arg)\n- `glob`: file glob filter\n- `case_insensitive`: boolean\n\n**Params**: `path`, `mode` (content|files_with_matches|count), `glob`, `type`, `case_insensitive`, `before`, `after`, `context`, `multiline`, `head`, `offset`.",
+  "prompt": "## file_grep\n\nSearch file contents with ripgrep. Capped at 50 matches by default.\n\n**Args**: `pattern` (required), plus optional named params.\n\n```\nfile_grep(pattern=\"pattern\", path=\"/abs/dir\")\nfile_grep(pattern=\"TODO\", path=\"src/\", glob=\"*.go\", case_insensitive=true)\nfile_grep(pattern=\"func main\", path=\"/abs/path\")\n```\n\n- `path`: search directory (not a positional arg)\n- `glob`: file glob filter\n- `case_insensitive`: boolean\n\n**Params**: `path`, `mode` (content|files_with_matches|count), `glob`, `type`, `case_insensitive`, `before`, `after`, `context`, `multiline`, `head`, `offset`.",
   "args": {
     "type": "object",
     "required": [