refactor: modular .bashrc.d/ structure

- Rewrite .bashrc as minimal loader (34 lines → loads .bashrc.d/*.sh)
- Clean .bash_profile: single source, Apple Silicon/Intel brew path
- Add .bashrc.d/ with 7 topic modules:
    00_env.sh      PS1, OSTYPE, colors, pyenv
    10_aliases.sh  universal aliases
    20_functions.sh proxy, dbash, git helpers
    30_work.sh     work-host detection, LDAP, AWX, Juniper tools
                   (+ unified-hub-login with env-var creds)
    40_k8s.sh      kubectl completion + aliases
    50_ai_env.sh   WORKSPACE/DATA_ROOT/MODEL_ROOT paths
    60_dotfiles.sh dotfiles manager aliases, zet shortcuts
- Secrets (SN_PASSWORD, LDAP bind PWs, Unified Hub token) moved
  to ~/.bashrc.local (gitignored, written by setup script)
- Update .dotfiles_manifest to track .bashrc.d directory

.bashrc.d/50_ai_env.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+# 50_ai_env.sh — AI / ML workspace environment variables and aliases
+# Shared across all machines, profile-neutral.
+# ============================================================================
+
+export WORKSPACE="$HOME/workspace"
+export DATA_ROOT="$HOME/data"
+export MODEL_ROOT="$HOME/models"
+
+# HuggingFace cache
+export HF_HOME="$MODEL_ROOT/huggingface"
+
+# Ollama model store
+export OLLAMA_MODELS="$MODEL_ROOT/ollama"
+
+# Navigation shortcuts
+alias ws='cd $WORKSPACE'
+alias src='cd $WORKSPACE/src'
+alias data='cd $DATA_ROOT'
+alias models='cd $MODEL_ROOT'