feat: add Obsidian-style graph visualization

Implement force-directed graph view for visualizing note connections:

- Add graph data model parsing [[wiki-style links]]
- Implement Fruchterman-Reingold layout algorithm
- Create character-based canvas renderer with highlights
- Add interactive filtering by tag/folder
- Support navigation (h/j/k/l), zoom (+/-), and node selection
- New commands: :IdeaGraph, :IdeaGraphFilter

New files:
- lua/ideaDrop/ui/graph/{init,types,data,layout,renderer}.lua

Updated documentation in README.md, CHANGELOG.md, and llms.txt

lua/ideaDrop/utils/constants.lua

@@ -115,12 +115,15 @@ M.ICONS = {
 	SEARCH = "🔍",
 	TAG = "🏷️",
 	TREE = "🌳",
+	GRAPH = "🕸️",
 	SUCCESS = "✅",
 	ERROR = "❌",
 	WARNING = "⚠️",
 	INFO = "ℹ️",
 	SAVE = "💾",
 	REFRESH = "🔄",
+	NODE = "●",
+	LINK = "─",
 }
 
 -- Key mappings (default)
@@ -129,6 +132,78 @@ M.DEFAULT_KEYMAPS = {
 	REFRESH_FILE = "<C-r>",
 	CLOSE_WINDOW = "q",
 	SELECT_ITEM = "<CR>",
+	-- Graph keymaps
+	GRAPH_CLOSE = "q",
+	GRAPH_SELECT = "<CR>",
+	GRAPH_FILTER_TAG = "t",
+	GRAPH_FILTER_FOLDER = "f",
+	GRAPH_RESET_FILTER = "r",
+	GRAPH_TOGGLE_LABELS = "l",
+	GRAPH_CENTER = "c",
+	GRAPH_ZOOM_IN = "+",
+	GRAPH_ZOOM_OUT = "-",
+}
+
+-- Graph visualization settings
+M.GRAPH_SETTINGS = {
+	-- Layout algorithm parameters
+	LAYOUT = {
+		-- Fruchterman-Reingold parameters
+		REPULSION_STRENGTH = 5000, -- How strongly nodes repel each other
+		ATTRACTION_STRENGTH = 0.01, -- Spring constant for connected nodes
+		IDEAL_EDGE_LENGTH = 50, -- Ideal distance between connected nodes
+		GRAVITY = 0.1, -- Pull toward center
+		DAMPING = 0.85, -- Velocity damping per iteration
+		MIN_VELOCITY = 0.01, -- Stop threshold
+		MAX_ITERATIONS = 300, -- Maximum layout iterations
+		COOLING_RATE = 0.95, -- Temperature cooling per iteration
+		INITIAL_TEMPERATURE = 100, -- Initial movement freedom
+	},
+
+	-- Visual settings
+	VISUAL = {
+		NODE_CHAR = "●", -- Character for nodes
+		NODE_CHAR_SMALL = "•", -- Character for small nodes
+		EDGE_CHAR_H = "─", -- Horizontal edge
+		EDGE_CHAR_V = "│", -- Vertical edge
+		EDGE_CHAR_DR = "┌", -- Down-right corner
+		EDGE_CHAR_DL = "┐", -- Down-left corner
+		EDGE_CHAR_UR = "└", -- Up-right corner
+		EDGE_CHAR_UL = "┘", -- Up-left corner
+		EDGE_CHAR_CROSS = "┼", -- Crossing edges
+		EDGE_CHAR_SIMPLE = "·", -- Simple edge dot
+		MIN_NODE_SIZE = 1, -- Minimum node visual size
+		MAX_NODE_SIZE = 3, -- Maximum node visual size (based on degree)
+		LABEL_MAX_LENGTH = 20, -- Maximum label length
+		PADDING = 2, -- Canvas padding
+	},
+
+	-- Window settings
+	WINDOW = {
+		WIDTH_RATIO = 0.8, -- Window width as ratio of editor
+		HEIGHT_RATIO = 0.8, -- Window height as ratio of editor
+		BORDER = "rounded",
+		TITLE = " 🕸️ Graph View ",
+	},
+
+	-- Colors (highlight group names)
+	COLORS = {
+		NODE_DEFAULT = "IdeaDropGraphNode",
+		NODE_SELECTED = "IdeaDropGraphNodeSelected",
+		NODE_ORPHAN = "IdeaDropGraphNodeOrphan",
+		NODE_HIGH_DEGREE = "IdeaDropGraphNodeHighDegree",
+		EDGE = "IdeaDropGraphEdge",
+		LABEL = "IdeaDropGraphLabel",
+		BACKGROUND = "IdeaDropGraphBackground",
+		FILTER_ACTIVE = "IdeaDropGraphFilterActive",
+	},
+
+	-- Node size thresholds (degree-based)
+	NODE_DEGREE_THRESHOLDS = {
+		SMALL = 2, -- 0-2 connections = small
+		MEDIUM = 5, -- 3-5 connections = medium
+		-- > 5 = large
+	},
 }
 
 -- Notification messages
@@ -146,6 +221,12 @@ M.MESSAGES = {
 	NO_ACTIVE_FILE = "❌ No active idea file. Open an idea first.",
 	PROVIDE_TAG = "❌ Please provide a tag name",
 	PROVIDE_QUERY = "❌ Please provide a search query",
+	GRAPH_BUILDING = "🕸️ Building graph...",
+	GRAPH_LAYOUT = "🕸️ Computing layout for %d nodes...",
+	GRAPH_COMPLETE = "🕸️ Graph ready: %d nodes, %d edges",
+	GRAPH_REFRESHED = "🕸️ Graph refreshed",
+	GRAPH_NO_NODES = "🕸️ No notes found to visualize",
+	GRAPH_NO_SELECTION = "🕸️ No node selected",
 }
 
 return M