"Attempt to concatenate local 'note_path' (a table value)" upon "ObsidianOpen <char>"

### 🐛 Describe the bug

I get the following error when trying to get cmdline completion for `ObsidianOpen` when inside my Vault or not. I am using cmp and have noice (with cmdline UI) installed, though I don't think that interferes here. With Noice disabled, I get the same error.
```
 Error 11:50:43 msg_show.lua_error ObsidianOpen N Error executing vim.schedule lua callback: Vim:E5108: Error executing Lua function: ...kages/start/obsidian.nvim/lua/obsidian/commands/init.lua:117: attempt to concatenate local 'note_path' (a table value)
stack traceback:
...kages/start/obsidian.nvim/lua/obsidian/commands/init.lua:117: in function <...kages/start/obsidian.nvim/lua/obsidian/commands/init.lua:85>
[C]: in function 'getcompletion'
...eovimPackages/start/cmp-cmdline/lua/cmp_cmdline/init.lua:136: in function 'exec'
...eovimPackages/start/cmp-cmdline/lua/cmp_cmdline/init.lua:202: in function 'complete'
.../pack/myNeovimPackages/start/nvim-cmp/lua/cmp/source.lua:326: in function 'complete'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:299: in function 'complete'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:169: in function 'autoindent'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:161: in function 'on_change'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/init.lua:346: in function 'callback'
.../myNeovimPackages/start/nvim-cmp/lua/cmp/utils/async.lua:165: in function <.../myNeovimPackages/start/nvim-cmp/lua/cmp/utils/async.lua:163>
stack traceback:
[C]: in function 'getcompletion'
...eovimPackages/start/cmp-cmdline/lua/cmp_cmdline/init.lua:136: in function 'exec'
...eovimPackages/start/cmp-cmdline/lua/cmp_cmdline/init.lua:202: in function 'complete'
.../pack/myNeovimPackages/start/nvim-cmp/lua/cmp/source.lua:326: in function 'complete'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:299: in function 'complete'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:169: in function 'autoindent'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/core.lua:161: in function 'on_change'
...ir/pack/myNeovimPackages/start/nvim-cmp/lua/cmp/init.lua:346: in function 'callback'
.../myNeovimPackages/start/nvim-cmp/lua/cmp/utils/async.lua:165: in function <.../myNeovimPackages/start/nvim-cmp/lua/cmp/utils/async.lua:163>
```

### Config

```lua
require("obsidian").setup({
workspaces = {
{
name = "notes",
path = "~/Documents/Vaults/notes",
},
},
completion = {
nvim_cmp = true,
},
})
```
and
```lua
-- ftplugin/markdown.lua
vim.opt_local.conceallevel = 2
```

### Environment

```
NVIM v0.10.2
Build type: Release
LuaJIT 2.1.1713773202
Run "nvim -V1 -v" for more info

Obsidian.nvim v3.9.0 (unknown commit)
Status:
• buffer directory: nil
• working directory: /home/max/Projects/nvim
Workspaces:
✓ active workspace: Workspace(name='notes', path='/home/max/Documents/Vaults/notes', root='/home/max/Documents/Vaults/notes')
Dependencies:
✓ plenary.nvim: unknown
✓ nvim-cmp: unknown
✓ telescope.nvim: unknown
Integrations:
✓ picker: TelescopePicker()
✓ completion: enabled (nvim-cmp) ✗ refs, ✗ tags, ✗ new
all sources:
• nvim_lsp
• nvim_lsp_signature_help
• luasnip_choice
• luasnip
• async_path
Tools:
✓ rg: ripgrep 14.1.1
Environment:
• operating system: Linux
Config:
• notes_subdir: nil
```

The commit is `14e0427bef6c55da0d63f9a313fd9941be3a2479` (from nixpkgs-unstable) and I can assure you that all dependencies are installed.

Start in lua/obsidian/commands/init.lua at the reported line 117 and trace the ObsidianOpen completion callback around line 85. Reproduce completion with the supplied configuration and inspect the value passed to the failing concatenation. Done means ObsidianOpen completion no longer raises the table-value error, with completion behavior preserved.

Written by the indexing model from the issue text.